For the grenades SAF uses, the pin needs to be twisted and
pulled, and even then its pretty tight. I reckon you could use your
teeth, if you had a jaw like a pit bull and teeth made of steel. If
not, I think you're better off using your hands. It took me a good
ten seconds of wringing, twisting and grunting to get the pin off
the first time I threw a SAF grenade. Then again, I am quite
skinny, so it could have been a case of muscle (or lack of).
As for the deformation of a bullet hitting a target (or body), I
suppose a projectile might just avoid deformation provided that
most of the energy has been dissipated, but there is just enough
for it to embed itself in the target. So, I suppose a possible
scenario which may apply is if the target is hit just outside of
the effective range of the bullet, where the projectile is almost
out of steam, and doesn't have the speed/energy to smash itself
into the target. Having said that, I leave you to figure out the
the odds of finding someone who has gotten a non-deformed
projectile dug out of them.
My 2 cents. 
Edit: Btw, we are talking about assault rifle rounds (e.g. 5.56),
right? I think somebody told me pistol rounds may not react the
same way or something...
