During the frantic endgame part(unlimited multiball) in Black Knight, I wasn't able to get the balls out of the shooter. Was even getting 2 balls in the shooter lane. The classic "push the plunger" hurts the palm of one's hand. You might look cool doing it, but it can hurt.
Also, in 1991, a T2 machine, MN state fair: I moved my hand from the sides of the machine up, rubbing a little to close to it. It cut my hand on the metal edge and was bleeding a bit for the rest of the day.