IDF, and a pilot, so my grenade throwing was limited to the three live grenades we threw in our equivalent of basic training. We did not take it terribly seriously, in that, as pilots, we knew that if we were throwing a grenade, we had screwed up rather badly and were probably going to die. (Also, they did not give us grenades, as ejection seats and grenades are a bad combination.)
During said training, a young idiot (not me, but it could have been) screwed around with a practice grenade by attempting to pull out the pin Hollywood style with his teeth.
Pulled his canine tooth clear out.
Ouch!
Reminded me of a story I once heard about some guy serving in the Pacific in WWII who tried to fire a captured "knee mortar" by doing what seemed to make sense, by resting the base plate on his thigh!
Apparently, even though it kind of looks like that should work, that wasn't how it was used by the Japanese, and doing so would break your leg pretty efficiently (Don't know if that is true, but I have heard that story more than once!)