a person who is always playing practical jokes or likes to entertain a group of people by doing extremely random things.
Brendon and Joe could tell Brian was in a very playbaby mood due to the fact that he began to prank call people and throw wet mariscos at unsuspecting people
a person who games (or plays games) excessively, to the point of ignoring professional and social responsibilities or who becomes plain annoying.
"Renzo, stop playing Mafia Wars. You're such a play baby."
A person with a jones for competition of any and all types.
My ex husband is the biggest playbaby I've even known.