I share all of mine with the ones already posted, especially the foot fetish one. I don't judge if one is into that sort of thing, but feet creep me out. I refuse to have a foot that's not my own touch me. lol I'm not even overly keen on my own.

Moving on to my own:

I don't understand how the "pull and pray" method is still around whatsoever. That offers virtually zero in the way of safe sex.

I don't understand "sounding," or how that could be viewed as remotely pleasurable. It seems like it'd be seen as a picture next to the word "pain" in the dictionary.

While possibly a rewording of Doc's point, I don't understand how men who haven't lost their virginity ASAP are seen in a negative light, whereas women who have lost theirs are seen in a negative light.

I don't, in any way, understand the point of the hymen. Granted, I wasn't exactly asked for my input for the design of the human body, but as a guy, I'm fearful of having to potentially deal with that...the notion of hurting her "there" just doesn't really...compute, for lack of more eloquent phrasing.