Many bodily function shouldn't happen when brushing your teeth (sneezing is big one) but the latest one I learned is that burping your coke is also less than ideal. It. will. Burn. Your. Eyes. Any others I haven't had the joy....
A sneeze could cause your toothbrush to penetrate the roof of your mouth behind your palette. If that happens, don't pull it out on your own. Go to the ER immediately with it stuck in there. I know this because it happened to a friend.