Actually, the second definition in the Urban dictionary is almost perfect for MN - I'll C&P to spare delicate types the first:
The act of being fummy. To bludge. What one does at work after Friday's pub-lunch. Doing bugger all and dragging everyone else down with you.
Another, less common, form of fumming involves sitting next to a colleague while he is on the phone to a customer and scrawling all over his notepad whilst giggling. The notepad should end up containing a crude caricature of the colleague's sister with the words, "Please wear pants to my party" in a speech bubble. This slightly more obscure form of fumming can often be the most effective as both parties usually end up imploding in a fit of giggles.
We're online fummers, aren't we?