Any question answered...

It's an extremely annoying pejorative term which a lot of people on this forum (and probably beyond) use to try to differentiate themselves from people whom they perceive to be (essentially) 'bad cyclists' in one way or another. The term is meant to deride the alleged riding style of some people claimed to be 'nodding' their head while riding, but the meaning extends beyond that to just about everything that people do wrong in traffic. It's ultimately quite empty and just says 'I'm not like you'.

I have actually seen someone nodding as they went along on a (rather nice) road bike, though. It does happen!