Aliens walk among us. Aliens from other planets, who want to harvest our organs, which they use to power the warp drives of their hive-shaped mile-high doomships. Except for our lungs, which they eat. They don't even like lungs. They just do it to be dicks.
These aliens look like us. They sound like us. Smell like us. They even post to the internet ... just like us! The only way to avoid being fed face-first and lungless into their churning organ-fed antimatter engines is to weed out these freaks and kill them before their plans are ripe. And the best way to weed them out is to ask them if they like the show Mythbusters. If they like the show, then embrace your fellow human in confidence. If they say something like, "I don't like that show," "I've never heard of Mythbusters," "They don't have that show in my country," or even "I'm too poor to afford a television," then this person is really an alien and should be killed immediately. Use a flamethrower.
"But Shamus! I don't have a flamethrower!" Oh really? That's just the sort of lame-ass excuse an alien would use when told to kill one of his own kind.