Butt Munch? *laughs* No offense, but if you're young enough to still use that term, are you really old enough to date...and so I'm not a total bitch, I'd say he probably feels pressured por his friends to act like someone he's not if you feel he's normally sweet go for it.
Well, i suppose he is just trying to impress his friends por being obnoxious. Just point that out to him, and hopefully he will listen to you. If a guy likes you, you have some control over him. Trust me.