(expletive) Any thing (esp a male person) deemed to be vaguely useless, lacking real quality or consistency, or just plain old usefullness. Used as an amplification on the well worn 'cunt' insult. Possibly more insulting.
(1) My slowest PC is a useless Rubber Cunt of a thing.
(2) The rubber cunt that opens the fucking newsagent didnt show and I spent an hour in the fucked out rain waiting for him.