An uber-cool and ravishingly good looking internet forum dweller who flits between threads like a skylark betwixt the clouds, posting seemingly off-topic missives about monkeys, dolphins and highwaymen with like-minded souls, much to the annoyance of other forum dweebs.
This is called "thrashing". Those who do it are "thrashers".
Poster 1 : What do you all think of the latest series of This Is Your Life
Poster 2 : It's excellent, but I wish they'd do Derren Brown
Thrasher 1 : What is your favourite type of monkey?
Poster 1 : What?
Thrasher 1 : I prefer the bonobo.
Poster 1 : ARGH :madsmiley:
Poster 2 : HELP :sadsmiley:
Thrasher 1 : God I'm handsome.
MODERATOR : You're banned Thrasher!