I dunno what to tell you really. I mean there are guys who take indecent liberties, and guys who don't. Your friend is one who does. Seems like there is plenty of evidence out there statistically speaking to suggest that it is an escalating behavior as well.

Feeling wierd about it probably comes from being friends with the guy. Letting it go is one thing, but expecting that it won't happen again in a similar situation is probably not a good idea.