[ummonk]

A) Puking is not anywhere near as disgusting, and you could get equally disgusted by seeing someone peeing on someone else even in a nonsexual context (e.g. hazing).

B) Some people can feel elevated disgust towards portrayals of other people being sexual. In that case, the fact that it's sexual does make the difference, but it's still a disgust reaction.

[mclehman]

Point A is far more subjective than you're making it appear. Personally, puking is far more effective at provoking a reaction of disgust.