Guys, if your friend likes a girl, is she off limits?

Yeah. Usually.

Different scenarios,

1. I like a girl and my friend likes the same girl; there's gonna be a bit of friction between us until one of us backs down, or its obvious the girl prefers one over the other.

2. I like a girl a lot and my friend doesn't seem to like her as much but is still flirting with her, I'm gonna try to tolerate it for a while but if it persists I'm gonna tell my friend to back off.

When a guy likes a girl, its respectful for other guys (specially friends) to not show interest in that girl. If they both like her a lot there could be competition. So yeah, she's "off limits" unless we both really like her :P.

But you say he got annoyed when he just LOOKED at you. That's excessive if you ask me. If he was checking you out maybe, but other than that no.

The easiest answer to this is Yes. You don't move in on your friend's turf.