throw salt in my game
When someone tries to ruin a good thing for another, such as when I'm trying to talk to a fly young honey and then my boy comes up behind her and says, "You know this dude is 48 years old, right?." If that ain't throwing salt in my game, nothing is...BITCH!!!
As in the above example, you might say to your homie, "Damn, playa!!! Why you throw salt in my game?!?!?!?"