Professional chefs/culinary students, what was the biggest “Nope” you saw another chef doing in the kitchen?

Culinary student, just starting out

Someone in another group was grating cheese into a mixing bowl for spinach dip, when he suddenly shouts “Ow!” and a tiny bit of red formed around the cheese

He did not report to the head chef nor did anyone else, needless to say I stayed away from the spinach dip