Indian engineer who stood on the toilet and shit all over the floor, walls, etc. Building security had to stake out the place to find who was leaving the poop bombs.
One guy started quietly swearing to himself and shaking most of the day, like he had torrets. Neighboring employees began to develop a healthy fear of him. We find out that he hasn't been doing anything, that he had lied on his resume, and was previously a local chef who had become semi-famous for having not one, but two entire staffs simultaneously walk out on him (the second time, causing his restaurant to shut down).
An executive quietly embezzled a million dollars while on a five year gambling, cocaine and hooker streak. He will be starting his prison sentence soon.
A bunch of people for non-performance. Basically show up, have no clue what they are doing and try to fake it. They always get caught. ALWAYS. Their coworkers turn them in and sometimes clients, too.
I had an engineer working for me one time who coded a SQL server column containing currency as an integer. Rounding off cents wouldn't be so bad, except most of the cells contained values less than $1.
Oh, I almost forgot porn girl! We were at a trade show one day and while walking home at about 2am, we saw a girl literally lying in the gutter. We were laughing at her when we realized it was one of our employees. She had a habit of drinking way too much and going home with random strangers (sometimes she didn't make it home, a bathroom, bus or even outdoors would be fine). Anyway, we ended up firing her and later found amateur porn on her work PC (along with naked pictures of her and her sister).
Those are the ones that stand out most. I'm sure there are others.