brutus
Someone who is a Brutus is a very good friend who gives you the screw job.  This is derived from Julius Caesar's best friend. His best friend Brutus was the last person to stab the dictator Julius Caesar's last words were "Et Tu, Brute?" which means "You too Brutus?"
Jane; Lets fool around my parents are out of town
John; I'll be right over
Harry; Hey John did you tell her you got a girlfriend?
Jane; Get out of here
John; Thanks a lot Brutus