Oh and git has a hard-g like "green", not a soft-g like "gerbil".
You would only say it to a man - I'd only say "git" to a older man - and "get" to a male teen or a young man.
In the Harry Potter books Ron says "git" a fair few times, referring to Snape which is fine, and Draco which is jarring as it's not something teenage boys call each other. Of course what teenage boys *do* call each other may not be suitable for children's literature.