I have seen some doozies...
There was on place in London where the waiter came into the kitchen and wanted to slice the table bread on the board I was prepping raw bacon on... I worked there 4 hours
Then there was the place where the smoking area was in the potato/onion storage room, I worked there 2 days
And the place that didn't care if the chefs came to work already in their uniforms, I worked there one week..
What I can say, is that it's generally not that easy to "do" stuff to food, there are lots of other people around you and it would be very obvious, everyone would have to be in on it and that would be difficult...
Now, the stuff that chefs do to each other in the kitchen, that's another story all together, but it never crosses the lines into the customer food!