Here's why I find this question annoying.

What am I supposed to do even if he does that besides moving far away from him with my girlfriend? If he doesn't respect the boundaries of a girl regardless of she's single or in a relationship, he wouldn't respect the guy who's with her. I'm most likely to get a beating if I confront a guy like that.

Besides, unlike what the media shows, men are not violent at all. When it comes to situations like that we prefer to cool it down with words more than our fists. We avoid violence at all costs. Yes, there are violent men (same as women) but we hate them as much as anyone else in the world.

This is not a Stone Age era where it's the survival of the fittest and you can only stay in the "pack" if you show dominance. We are way ahead of that time and we don't have to prove our manliness to anyone.