This comes from a story about a highschool that had a fence in the back where it's students would go to behave innapropriately. The female would put their backs to the fence and then grip the fence with their hands, the idea was for the guys to basically molest the girls who had come up against the fence.
Now it can be used to describe any slutty girl or jerk-off male.
Person Two: "Fucking dirty fencer."
A term given to a person/people engaged in Male homosexual behavior in which the two gentlemen are using their male parts as swords in sexual battle against each other with very arousing results.