SUM
"SUM" is a shortened direct command with a meaning similar to "be quiet"', but which is commonly perceived as an angrier and more forceful demand to stop making noise or otherwise communicating. The phrase is probably a shortened form of "shut your mouth up", and its use is generally considered impolite.
Laura: I'll really hate rain, it scares the hell out of me. I mean were does it come from, can you drink it?

Dude: SUM bitch!