A male in a group of female friends who's job is to stop other males trying to score with the females in the group. Done purposely because the girls either already have a boyfriend or just don't want to be annoyed that night.
The cock-blocker can be either a male friend, or someone hired (almost like a bodyguard).
Popular methods of the cock-blocker include:
* Switching places with the female.
* Grinding with the offending male.
* Kissing the female to let the male know she is unavailable.
* Jumping in between the male and the female.
* Shoving the male, or squaring up to him.
* Warning him off with gestures.
John became the designated cock-blocker for the night after Mandy decided to go out with the girls and didn't want to be pestered by guys.