Peepz who kill the fun by wanting to do something else or calling it a day/night too early (like me).
"Ay I gotta go. I gottta see my friend so...just watch the rest of GLADIATOR without me, aightz?"
"You're such a KILL JOY!"
People who are douche bags and have to ruin the fun of everything, kill the mood or shoot everything down.
Jamie: "Naw, I think I'm going to skip out on the concert, chillin' with friends and going camping."
Caitlin: "Jamie you're such a fuckin' kill joy!"