Navel grazing: This occurs when an individual spends too much time posting tedious, argumentative drivel on STW and not enough time riding a bike.
The lack of exercise occasioned by this sedentary, housebound pursuit encourages the growth of a huge gut. When they get round to riding their bike, their Lycra top will no longer stretch round it, exposing the belly button.
Once out on the bike, for lack of practice, or bike maintenance, they have a spill and end up over the bars, skidding along the trail for a bit. With no lycra there to protect the exposed belly, navel grazing occurs.
So if you want to avoid navel grazing, get out on your bike more, and stop sitting in the house posting tedious, argumentative drivel on STW.