I very, very seldom complain about food or service..
When it comes to restaurants I vote with my wallet.. Bad service or food means a much smaller tip(but I always leave a tip).. And because everyone has bad days I will always give a restaurant a 2nd chance, if it is bad the 2nd time then I never ever go back.
There's 4-5 restaurants around where I live that I won't ever go to again because I had 2 bad experiences with them.. There's plenty of other restaurants to pick from.