I would probably call it sexual assault if I was going to call it something. It's possible that on his end it was a mistake, he was drunk, he didn't hear you, whatever -- but even if he didn't mean to hurt you, you're still feeling angry and disgusted, and those feelings are completely valid. Some people like your girl friend might be okay with what happened, but you're not -- that doesn't make either of your feelings about the situation any less real.

If this is a friend of yours I would talk to him about it and explain that you ended up feeling upset and confused about it. Just because you took off your top doesn't mean he gets to try and put his hand down your pants, and just because you joked for him to prove his size doesn't mean you asked for him to try and rub himself all over you (he could've just shown you, for example). If you want to remain friends I would talk to him and explain that you felt disgusted, and, if you worry that this could happen again, that maybe in the future it would be a good idea for both of you to not get that drunk with each other because of things maybe going too far. This friend may not be a safe person to drink around/be around when he's drunk, especially since your friend said he's done that to her as well.

Good luck.