usually just written as nmjb, jarra being local slang for Jarrow, a particularly deprived area of Gateshead with some right radgies, most of them entirely unable to reliably connect to an enterprise message bus.
He's not getting any messages? Nah it's not a bug he's just a nee message jarra bellend.
A retards pernouciation of retard. Usually used in the context of calling someone a retard. Used with the hand jesture of pulling the thumb and index finger against the upper part of your chest.