I've worked commercial refrigeration repair for 30 of the last fifty years. Commercial reach in boxes, walk in coolers & freezers. You REALLY don't want to know.
I had put some examples here but decided they were too much.
Oh, yeah. My ex-BIL did a lot of plumbing and HVAC work at restaurants, and has some horror stories.
Of course, I worked as a dishwasher at a "family" restaurant when I was in high school. Here are some of the highlights:
1. "Dirty Dave" made the 1000 Island dressing. He'd start with the usual ingredients, then for flavor he'd spit in the pot a few times. He'd take a black, greasy rag that was used to clean the floors and stir the dressing with it. He threw in other stuff, but I forget what.
2. We'd get the chicken in 50 pound boxes, frozen. We'd unload them to the basement, then have food fights with the wings, thighs, breasts, etc. When we were done, we'd run the pieces through the dishwasher to clean them up before breading. Did the same with steaks, too.
3. One night at the soda fountain/ice cream station, the cockroaches came in waves like you see the Viet Cong do in the movies. It was like a sea of brown.
There was more, but nothing beats what happened at a drive-in restaurant in Downers Grove, IL. A friend of my best friend worked there. Another guy used to put "his own secret sauce" on burgers. I think you know what I mean.