This is more like a etiquette lesson video, but I liked how it was done so… here it is: Tips on how to send food you didn’t like for some reason, back at a restaurant for replacement or refunding.

I should take notes.. usually, when the foods taste bad I just don’t eat and never go back to the restaurant.
If it’s rotten, have some foreign object in the middle, or something like that though, I complain, and not very politely (unless it’s an honest simple mistake).

Source: Lifehacker