Catching bullets in your teeth is a magician's trick, and can't be done for real (after all, Kung Fu films are not renowned for their slavish adherence to the laws of physics...)
A bullet has a great deal of energy. When it stops, that energy has to go somewhere. Stopping a bullet dead with your teeth would send the teeth the other way almost as fast, in bits, and the bullet would probably still have enough energy to make a big hole in your head (an arrow has a lot of energy too).
This is actually how bullets do much of their damage -- the energy is dumped into your flesh, and it either breaks things, or in the case of high-velocity bullets, the water in the flesh is flash-boiled causing an explosion which does even more damage.
A bucket of water might be good for stopping a slowish bullet, if you happened to have one handy and held it in just the right place...
Your best bet is to hope that the ignorant bas*ard who has the gun is a rotten shot.