The easy thing to do is be dismissive with him, don't try to fight him at all, don't be spiteful or show animosity, just be friendly and uninterested in the negative things he says about you, and normal and friendly when it comes to conversation that isn't negative towards you. Don't laugh at things he says that are at your expense, but don't get upset either, just stay cool and ignore, if he keeps pressing it just stop talking to him or respectfully ask for privacy by asking him to leave.

If it's some girl you barely know, you can also do the counter intuitive thing and simply ask him if he likes her, explain that you like her but you didn't realize at first that he had a thing for her and you'll let them talk alone and won't get in the way if that interests him. Then guy will either deny he likes her and you're up, or if he goes the other route, you just leave and wait until he fails or gives up, then go back.

If you simply want to have a pissing contest for what ever reason, just stand between him and the girl you like and talk to the girl and ignore him until he goes away. Getting into this shit though and pushing it can just lead to him doing more of the same and you both looking bad socially, or you and him buying into a verbal ball busting fest that can just lead to a real fight to see who has the bigger nuts.

But what about those guys that get REAL amog? They kind of are friendly and funny guys, but sometimes they make jokes about you, call you a virgin whatever. I'm talking about a guy in my gym who when he shaked my hand squeezed it so hard I thought it would break, but there was nobody there. If there was a woman I would be screwed.

These hunky meatheads are pretty unbeatable since you can't confront much.