One who will do anything to further his own personal interests without regard for the impact his actions will have on the interests of his "friends" or colleagues. Buddyfuckers cannot be trusted to "do the right thing" and have no regard for abstract principles such as ethics or morals.
This title is used frequently in the U.S. Naval Aviation community. When speaking discreetly, Aviators may say "buddy is only half of a word."

I can't believe Brad tried to steal my job just so he could get a bonus; he is such a buddyfucker!

I can't believe Brad tried to steal my job just so he could get a bonus; to him, buddy is only half of a word.