I have a male college friend with Asperger's. Even before he'd ever heard of the diagnosis, he was entirely cognizant of the fact that he didn't always pick up on the social cues other people considered obvious. In terms of sexual contact, he dealt with this by conscientiously seeking consent even for relatively minor gestures of affection (i.e., "I would very much like to hug you. Would that be okay?") Moreover, if you tell him explicitly that you never wish to discuss the subject of one of his obsessions with him again, he will remember and conscientiously abide by this request.