a person with downsyndrome.
mainly because they dribble and spit all over their gobs so it becomes wet and or crispy.
you could also call someone a wetgob if they look like/act like they've got downsyndrome ( really ugly, speak like one, fat bottom lip etc)
Carlo: Adam looks like he's got downsyndrome
Luke: Adam you look like a wetgob with all that round your mouth.
Adam: splish splash splish splush.