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