Never by my piranhas but...
Back in my drinking days , I reached into my 8' Burmese Pythons cage to move the water dish that the rat was hiding behind and wham!! I had a mouthful of teeth sunk into my hand just above my thumb. Bottom jaw was into the palm of my hand and the top was over the top of my hand and the snakes had three wraps around my wrist and arm. I tried the dog trick of putting my finger and thumb of my left hand into the corners of the snakes mouth and ended up with my index finger and thumb stuck on the rear teeth in the pythons mouth. As soon as I picked her up from the cage she released. I was pouring blood from the forth rows of teeth on the top of my hand.
Ahhhh , the snake days....
I was nipped once by my 3' Spectacled Caiman too, just a nip and release.
both were alcohol related.
I've had far fewer "Stupid Human Tricks" since then.
I'm not looking forward to a bite from a Piranha so I'll be as careful and attentive as I can when dealing with them.