Shut Your Fucking Cock-Port.
The same as STFU, "Shut the fuck up!"
Or, "Shut your mouth!"
Cock-port, meaning mouth.
Zack: I'm not fat. I'm just big boned.
Brian: No, I'm pretty sure you're a fatty.
Cass and Chels: SUFDUG!
Cass: Brian, we know Zack is fat.
Cass and Chels: NUMOLOP!