Ohoh...

I can remember once when I was watching my brother play san andreas and witnessing this games pretty ridicules AI.
So he was driving along the road, when this guy suddenly throws himself from the sidewalk and out into the road right in front of my brothers car in an apparent attempt to dodge his car.
Much laughter to follow.

Also: pretty much every cutscene in conkers bad fur day.

OP, I agree. Citizen Kabuto is hilarious. I keep wanting to say halo but its purely because of Red vs Blue and not anything to really do with the game.

FFVII at the Honey Bee Inn (house of ill repute). My mum walks into the room not looking or paying attention to what is on screen proceeds to sing along with the song playing since it sounded sort of bubbly. .... eehhhhh

The rebel password in HL2Ep1.
"I'm not gonna even tell you to Shut up.".

Rik Mayall's commentary on Hogs of War.

Sexual Harassment Panda:
OP, I agree. Citizen Kabuto is hilarious. I keep wanting to say halo but its purely because of Red vs Blue and not anything to really do with the game.

My name is Michael J. Caboose and I... HATE... BABIES!!!!!

Star Trek Legacy (I know, I know...) has some great moments of unintentional humor.
"Fool! You're clearly outmatched!" He says as his ship is exploding.

On that note, the game can be oddly formal about how people announce their own deaths:
"Poseidon to fleet: AAAAARRRRRRRGGGGGGHHHHH!!!!!!"

Probably not my favorite moment ever, since i canīt remember that right now, but i was playing Oblivion a few days ago and engaged some bloody Cat-Faced Bandit with my Mace of Facesmashing, anyway he stepped backwards onto on of these traps and a giant morning star fell from the ceiling and killed him. Ha!

Aight, sorry if this is a bump, but the other, newer thread got locked, with a link to this one so...

Just recently: Was playing Use Map Settings on Battle.net, and there's a genre of maps called "Diplomacy".

I was playing a game set in Europe, was Belgium, with a German ally. Eventually, he becomes a super-power, everyone else has left, and I barely have France*. He then un-allies me to end the game, because he could.

He destroys my base, all my workers, and all but two Supply Depots left. I vis'd him again so he could kill me off.

He left before he did, leaving me, a first-time Belgium player with only 2 depots left from a massacre, the only one remaining. I won a game while on the brink of death.

I am one lucky bastard, really. =P

*Yes, I know I suck. Shut up.

Recently, my brother and I were trying out the multiplayer in GTA IV for the first time (my brother lives in Wales, I live in Chicago.) Of course we originally intended to do one of the multiplayer games, but our faffing about was much too fun to be bothered with any organised mission. Anyway, we were at a baseball diamond attempting to play baseball with a live grenade: one person cooks grenades and throws it at the bases, the other is in a car at home and must round the bases without getting blown up.

After doing this a few times we were both rolling with laughter (and Guinness) at ourselves and it was my turn to lob grenades. I asked my brother if he was ready, and he said, "Sure, toss me off." Being the cheeky bastard that I am, I quickly switched to the RPG and threw him a strike in the form of an exploding-car-curve-ball.

I haven't laughed so hard with him since we had a crayon war with our neighbours many, many years ago.

sicDaniel:
Probably not my favorite moment ever, since i canīt remember that right now, but i was playing Oblivion a few days ago and engaged some bloody Cat-Faced Bandit with my Mace of Facesmashing, anyway he stepped backwards onto on of these traps and a giant morning star fell from the ceiling and killed him. Ha!

In a similar moment, I had the bad luck to be facing three necromancers once. Each of them was using the annoying technique of "summon something squishy with fists and then run as far away as possible while it pummels you to bits". Unfortunately this was proving effective - I was taking a pounding. Ignoring the zombies, I went for the necromancers, who kept running away despite the fact that a single hit with a mace would probably have done for me at that point; when all three ran, one at a time, into a nail trap, and each one died instantly. Ha! Ha! Ha!

This is an easy one for me, seeing koichi play Ino in the Japan 23 turning a Japanese guilty gear tournament into a personal combo video, oh Koichi why are you so amazing with Ino.

In Brawl my friend great aether me with a soccer ball and I took twice the damage and went twice a far it was awesome.

Watching someone I want to be the guy on their first try (google it if you don't know what I am talking about)

Lets play La-mulana.

Battlefield 2142 online. I was on Suez Canal in the attack chopper when the other teams chopper decided he wanted to kill me. We both eventually went into hover mode and he was lowly edging backwards while i hovered towards him. We were both waiting for our missles to reload and I was positive his would finish first.
All of a sudden he blew up... he had backed into one of the random towers in the map :)

Playing a map on Zombie Panic source which has a fridge where you're supposed to lock the opposing team in, and let them freeze to death over a period of a few seconds. This has made for many personal griefing sessions:

"Hey, there's ammo in there; go get it."
"Ok..." (gets locked it in) "...Hey, WTF!? LET ME OUT YOU JERK!"

By that point I'm too busy rolling around laughing as they slowly scream into oblivion to even consider opening the door; I really can be an arse sometimes.

The entirety of Lego Star Wars.

Putting cones on the heads of the zombies in Dead Rising.

The little robots spawned by the "glove of doom" in the ratchet and clank games. That evil laugh is hilarious. :) For that matter, any and all cutscenes in those games that star the plummer. "did he just slide down a sewer pipe?"

I'm sure I'll think of more as soon as I hit "post"

Sam&Max

-A unicorn! I will call him...Horny...

I laugh every time at that crack Barney makes at the beginning of Half Life 2:

"Great job turning that switch. I see that MIT education just pays for itself."

The first time I heard it, I involuntarily flipped him the bird.

The "Krogan Testicles" Schtick in Mass Effect. Youtube it. Guarantee you'll laugh yourself blue.

The "Krogan Testicles" Schtick in Mass Effect. Youtube it. Guarantee you'll laugh yourself blue.

The cutscene in SSBB's Subspace Emissary where, after Falcon punching the giant ROB, Captain Falcon skids to a halt, striking a pose and killing a crowd of Pikmin, as well as the awkward silence that follows.

The cutscene in Subspace Emissary where Lucario picks up Snake's box and the exclamation point appears above Snake's head.

Harpooning someone to a car in Crackdown and subsequently driving around with them attached to the car.

In Metal Gear Solid
when you surrender them,
I point at their crotch
and theyre like
"Please!!Dont Shoot!!!"
and i always think
"lol Priceless"

Ahh, good topic. Definitely in TES oblivion, I was doing a dark brotherhood mission where you have to kill some guy in the Imperial City. I attacked the guy, and he took out a sword and started attackin me. Some guards came in, and so I ran into the street. I was running behind some houses in their back yards, being followed by the target, and two imperial guardsmen. I turned around briefly to see what was happening, when the two guards, in an attempt to shoot me down with their bows, promptly delivered two arrows to the back of my targets head. He was in the unfortunate position between me and the guards, and got taken down hard. Stupid ass watchmen beat the mission for me! Hysterical.

madaseyer:
In Metal Gear Solid
when you surrender them,
I point at their crotch
and theyre like
"Please!!Dont Shoot!!!"
and i always think
"lol Priceless"

Well what would you do?!

I'd get on the ground in the foetal position, and try not to piss myself.

HL2: Lost Coast: I harpooned a combine. He went flying and doing backflips off of the map.

CoD4:
SAS1: We're going deep, and we're going hard.
SAS2: Surely you must be joking.
SAS1: I'm not joking. And don't call me Shirley.

I have pretty much found the storyline in GTA4 and Portal to be the funniest that I have played.

BadSnack:

Lets play La-mulana.

Two words: Skimpy swimsuit.
Best. Horrified scream. Ever.
EDIT: I just remembered- Trilby's rant with the doors in 5 Days a Stranger.

So many funny ones.
Dead Rising: I was using a bowling ball to kill zombies and then I lost it. I played for about 2 more hours, and then came a cross my bowling ball. I have no idea why this was hilarious at the time.
Halo: No matter how many times my friend and I try to beat it, we end up killing eachother most of the time. Also, I killed a Wraith with 44 Assult Rifle bullets and a plasma pistol. The snow turned green for some reason after. True story.
Not as many funnies as I thought...

In Oblivion, I once watched two Imperial Rangers attack each other with bows.

The funny part was when the survivor turned to me and said "Nice to see a friendly face in these dark times"

Funny moments, intentional:

The two guys in the mineshafts in Half-Life 2 Episode 2, Griggs and Sheckley.
"Sheckley!"
"What?"
"Sheckley!"
"WHAT?"
"...forget it."

"I think we misunderestimated them!"

And, as Freeman is finally leaving the mineshaft with Alyx and their Vortigaunt companion, this comes out of Griggs:
"Oh, and Freeman... be adequate!"
Sheckley stares at him for about two seconds.
"What is that supposed to mean?!"
"I don't know, it sounded like something the Vorts would say!"

Funny moments, unintentional:

The NPCs in Oblivion almost never seem to understand when they're overmatched or seriously in danger, especially when you've hit them with poison or some other damage-over-time effect.

"WHY! WON'T! YOU! UUUUGH!" *hit by trap*

"What's the matter, is the baby gonna oooof." *killed by poison*

It's also a thing of beauty when, in their eagerness to dodge some spell or arrow, they send themselves hurtling off the nearest cliff face. And then I remember that I can't loot their body when they do that. Argh!

Original Halo, Assault on the Control Room, when you have to cross a bridge near the end while two Banshees are flying over you. I was playing co-op with my friend, and one of the Banshees was flying at us so I whipped out the rocket launcher and blew it up. Then the smoking carcass of the Banshee comes falling down on my friend and he screams and throws a nade right before it falls on him and kills him. I was too busy laughing my ass off to realize the nade he threw bounced off the Banshee and landed at my feet, and since I had no shields at the moment... We were both laughing and swearing alternately for a few minutes.

Also, Banjo-Kazooie, way back in the 64 days. That game had the wittiest dialogue and some of the funniest enemies around. And of course, Time Splitters: FP, also for great dialogue.

The Rogue Wolf:

The NPCs in Oblivion almost never seem to understand when they're overmatched or seriously in danger, especially when you've hit them with poison or some other damage-over-time effect.

Oh, yes. Oblivion NPCs are not that intelligent, are they?

One time I was attacking the Mythic Dawn, and one of them goes "I'm not afraid to die".

Without skipping a beat, I say "Good for you." and stabbed him to death.

I have two suggestions
1. Hogs of war for PSX, the whole game is just hilarious
2. In Oblivion, the NPC that asks you "Do you know what the punishment is for necrophilia? Just out of interest"

EDIT:

3. Stealing the combine harvester in GTA San Andreas

In oblivion enchant a robe or something to make damage on yourself, then pickpocket a person and put the robe on him/her, and then if she/he wears the robe he/she is slowly going to die and it looks pretty funny

without a doubt, the wild bunny by sander cohen. that kinda bordered on hilarity and disturbance, but whats better then hearing old sander cohen go nuts like that?
"PLLLLEEAASSSEE TAKE THEM OFFF!!!! PLEASSSSSEEEE /WEEPS"

Summoner Geeks, i still laugh quite hard at it, if ya dont know what it is go on youtube :D