I'm sorry you got bit and didn't have your wits about you to react in a timely manner. Those hurt for a while as I recall the last time I was nipped and jerked as his teeth were clamping. Ripped a chunk of skin out just below my elbow and he thought I was about to eat him for all of about 45 seconds with the amount of bouncing and flailing I was doing. If the stall wall hadn't been as thick I truly believe he would have ran through it trying to get away from me.
It took a long time before he would even take treats out of anyone's hand after that episode. He NEVER even thought about getting his teeth close to skin after that.
Just remember you have all of about 3 seconds to react to an act on their part before it loses it's effectiveness.