It's not rude, but it's not polite either. You wouldn't use it with a person of senior social rank or someone you don't know well. You could use it with good friends - guys often use it with girls, as well as kids. It's colloquial but not offensive... unless you pronounce it as おめぇ then that starts sounding nasty.
A variant of おまえ is 手前 (てまえ), which is certainly not polite and is considered offensive when the pronunciation is slurred as てめぇ!