[carlosjobim]

No, restaurant workers will not mess with your food in that way. No matter what they think of you as a client. Ask people you know who have experience in that sector and they will tell you that such things are absolutely taboo. Anybody who did anything like that even once - or even suggests it - would be instantly fired and blacklisted in the community.

If the waiters or chefs hate your guts, at most they will swear in the kitchen.