We are not talking about food poisoning and those that can harm you like steel wool in your food and food allergy, etc. Just small harmless pet peeves that you still cannot accept to find about your food. And probably you may have much higher expectations for fine dining food, so lets not target those but may be we share our opinions about some average restaurant food.
To start off, I in particular don't like seeing that black line still there on the back of prawns when the prawns are peeled. If I ordered whole prawn, I don't mind to peel it and devein it myself. But if they are served peeled but not deveined, I will never order the same food from that restaurant again.