Microsoft insists that Xbox Live bigotry will net you a ban, no matter which group it's aimed at.
Last week, several outlets, including The Escapist, reported that players who use sexist slurs during Halo 4 matches would face a lifetime ban from the Xbox Live service. The media coverage of an interview with 343 Industry's Kiki Wolfkill and Bonnie Ross misinterpreted their statements to mean Microsoft was changing its online policies specifically for Halo 4 with a focus on sexism in particular. A Microsoft rep has since confirmed that this is not the case.
The rep also made it clear that Xbox Live policy is no more tolerant of homophobia, racism or any other form of bigotry than it is of sexism. However, the Xbox Live Code of Conduct does specify that "severe racial remarks," alongside modding, fraud, hacking and using your Xbox Live Camera to take photos of your genitals, can warrant an "immediate permanent suspension." Other forms of bigotry aren't mentioned in that passage.
Regarding general behavior, the Code of Conduct Reads as follows:
Don't create a gamertag, profile content, Avatar action, Avatar content, or in-game content that other users may be offended by. This includes, without limitation, anything related to or suggestive of: profane words/phrases, topics or content of a sexual nature, hate speech (including but not limited to racial, ethnic, or religious slurs), illegal drugs/controlled substances, or illegal activities.
We apologize for our contribution to the confusion on this matter.