Gun's Going Off

Used as an exclamation when a person with a penis is ejaculating. Comes from a comparison of a penis looking very much like a gun, and their cum acting like bullets being fired.

*person 1 and 2 are fucking*
Person 1- "Shit, I'm getting close"
Person 2- "Me too, baby"
Person 1- "Fuck, gun's going off (as they ejaculate)"