A term popularized by male college students. It can be used after one male asks another if he would like to do something (i.e. grab dinner, go out, etc.) and the other male denies his request. "Bro-blocker" can be substituted with "B-B."
Roommate 1: "Bro, we're all going to fourth meal, wanna go?"
Roommate 2: "Na man, I got stuff to do."
Roommate 1: "Dude, you're such a bro-blocker!"