Someone who consistently oversteps their bounds in an offensive manner. Such as taking the last beer when they didn't even buy it, using your car without asking, borrowing things without leaving any form of notification, pursuing ulterior motives with your significant other, secretly stealing your cigarettes or dip while you sleep or blatantly to your face, and similar actions.
Sven took the rest of the beer before we woke up! He didn't even buy it! What a Fence Fucker!
One who fucks on both sides of the fence; cannot make up their mind regarding their sexual orientation and thus switches their preferences constantly; (has nothing to do with bisexuals since bisexuals have actually claimed an orientation)
Dom, the fence fucker, who was gay just yesterday, was all over a group of girls saying, "I'm straight now."