I’ve had a few experiences . . . all in my high school years.
First I worked at Burger King for a few weeks back in the days of heavy polyester uniforms with big bubble caps. I was fired for taking vacation before my six weeks probation period was over. Other than that it was ok. I didn’t see anything weird or unhygienic.
Then I moved on to a local pizza place . . . sometimes on the grill, sometimes making the hoagies, sometimes at the ice cream counter. It was a blast, staffed by teens from the local boys and girls Catholic high schools. Owners lived upstairs and were very cool: the delivery guys would pick up beer on their last delivery that we could drink as we cleaned (but we had to pour it into the red plastic cups to be discreet That’s also where I learned to make pot pipes out of aluminum foil. Unfortunately, the hours sucked–during the school year we could be there until 1:30 or 2:00 and during the summer we sometimes had to work the day shift starting at 10:00, practically the middle of the night for a 16 yo. Not to mention, you always smelled like onions and grease at the end of the shift. Always cracked us up when guys tried to pick us up on the way home (maybe they were just hungry Again, never witnessed anything gross/unhygienic.
Finally, I worked as a waitress at an Italian restaurant run by two Greek families. They were nice but a lot tougher than the pizza shop owners. Quit after about three weeks as the clientele were fond of running the staff around, but not so fond of tipping.