Someone who was pissed on as a child. Typically, once a child is urinated on, a plaque (a "Pissbaby Plaque") stating the name of the child, the time and day it was pissed on and by whom is riveted to its back. Pissing on a young child renders them mentally retarded and greasy in complexion.
"Hey Joe, let me see your Pissbaby Plaque! I've gotta see who made you this dumb!"
"That guy is fucking dumb, he must be a pissbaby"