A male who either has sex with your girlfriend / ex-girlfriend, or hangs out with your girlfriend / ex-girlfriend all of the time. The act is called "pulling a brenze", and the recurring act is called "brenze disorder".
There are different phases of "brenze disorder" that vary in severity. These stages range from pulling a serious "brenze" all the way to "brenzenation". Someone who pulls "brenzes" a lot, or has "brenze disorder", usually has a part-time job, an annoying laugh, and a multicolored compact car.
Whilst the origin of the "brenze" is currently unknown, experts believe that "brenze disorder" is caused by a combination of bad hygeine and excessive video game abuse. This leads them to be unattractive, meaning the only females they can be around are their friends girlfriends, creating the perfect atmosphere for a "brenze".
Ex 1. "Dude, I just saw SOANDSO in the car with him! Dat dude is pullin' a serious BRENZE!!!!!"
Ex 2. "Bob: Chet, buddy, sit down on the couch and take a load off.
Chet: I'd love to, Bob, but your girlfriend is sitting on the other side, and that would mean I had BRENZE DISORDER."