Someone who is a bit of a phsycho and has obviously not got all the lights turned on upstairs. They are a bit wierd and obsessed with some disturbing things but are friendly really, its normally thier imaginary friends causing the trouble.
person:"who are you talking to rummy?"
rummy child:"Dennis, he's my imaginary friend, he says you look funny and he doesnt like you."
person:"oh, where is he standing?"
rummy child:"behind you with his pet axe."