Starting this off myself, there was one fella at my current job who bought vodka at a liquor store during his lunch break, poured heaps of it into his soda from a fast food joint, and wound up getting fired when they noticed him getting drunk as hell.
That was before I started working here, but coincidentally I met him at my other job!
Mine is similar. Arrived, day one in a new team; this one was more high-intensity than the usual - a fast-paced and very hands-on work environment. Noticed the team leader was working in a dysfunctional and unsafe manner; seemed unsteady. As the most junior member and a newbie at that I hesitated to confront directly; thankfully I managed to find a more experienced colleague. Scene was made safe; turned out the guy was drunk as a skunk. Canned within the hour.
I’ve since learned to be stronger and more willing to confront suboptimal or dangerous performance in team members, regardless of their seniority.
That was pretty scary.