There was a young (20 +/- 2 years) guy DLing in the gym. He was doing sets of 3-5 with a weight that was quite challenging for him. The issue: On every rep, he had his head turned all the way to the side as he watched himself deadlift in the mirror. I was sure that, at any moment, the torque on his spine was going to rip a transverse process off at the base.
The confession: Upon seeing this, I almost broke Gym Commandment #1. (‘Thou shalt not give unsolicited advice.’) Almost.