One who fucks hir partner while skidiving nude aiming for orgasm just as the shoot opens.
Charlie the freefucker hit up Hulga alright but due to her malicious groping, which loosed his parachutte harness, he soon found himself about to caress the gound.
A "Frat Fucker" is one who joins a fraternity... period. 99% of frat members or "brothers", are womanizing assholes who need to pay to have friends. Usually also have a small penis, or a weak personality, and use a fraternity to make themselves feel wanted or special.