Girl: Well I was thinking maybe we could...
Sibling/Friend: Hey guys hows it going?
Guy: Damn, You Boner Killer
"Yea man!! Its fucking tight.. i ran over a dog on the way here"
"Dude... Why you got to be such a BONER KILLER!!!"
"Who puked on your pool table?"
"Just some Boner Killer."
Example 1: You meet a cute girl/guy. They stink.You all of a sudden loose all attraction.
Example 2: Your at a party and your having fun. Then some idiot decides to start a fight. It gets out of control, the cops come over, and you get arrested. Your night is ruined.
Example 3: You have a crush on someone and then you come to find out something terrible about them (i.e. STD, hoe, player, too many kids, married). Ruins the image you had in your head about them.