The act of distracting another while they are
hard at
work or trying to concentrate on some very important task (
writing, surgery, bomb disposal etc).
"Cheers for that goatsnab. I nearly blew up the reactor."
Or go up behind a friend when they are
hard at
work, preferrably at a time when they definitely do not want to be distracted, grab their shoulders and
push down repeatedly (they should be sitting on a partially sprung chair, ideally), while saying 'Goatsnab, goatsnab, goatsnab!'