Very similar to calm yourself, it's what you say to someone who's acting up, maybe buggin, or in serious danger of going postal.
For maximum impact, use it as a complete sentence at the end of whatever else you wanted to say.
Paris: You borrowed my new skinny jeans without asking? I'll claw your eyeballs out, you thieving skank!
Lindsay: Listen beyotch, they needed breaking in by someone with some actual junk in the trunk. I'll wash 'em before I return 'em. Relax yourself.