knobstand
Knob is commonly used in Britain to mean penis, so the implication of knobstand is that someone is useless, that he serves no purpose other than to support his own genitals. Not in general use but sometimes heard said by teenagers in South Manchester. A few years ago I saw it in an Australian music fanzine, but I would assume this was written by someone with connections to Northern England.
Can't you do anything right? You knobstand!