Wind-Up Merchant (WUM)

I recently joined a Facebook group run by a British man. One of his rules was "NO WIND-UP MERCHANTS. (WUMs)." I had no idea what he was talking about, and so I consulted the Urban Dictionary:

"It refers to someone who posts on message boards and newsgroups with the intention to cause as much disruption as possible by goading others."

So WUMs are like trolls. I think I'll begin referring to some of our posters as WUMs.