I may either have a short memory, or have been lucky, but I can count the number of bad experiences I've had at restaurants, and still remember, on one hand. Unless the offense has been quite obvious - say, a big green caterpillar in my salad (happened once!), or a hair in my soup - I've never felt like lodging a direct complaint. The most I do is to call it a 'three-time experience' (an in-house joke) - the first, last and only time I'll go there.
I do wonder though if complaining would have done anything. I tend to shy away from confrontation, but eating out, especially at a high end restaurant, is a very special, not to mention expensive, occasion. When such an experience is screwed up, as it was for this commenter, it can be very frustrating to say the least.
What do you do when you have a bad restaurant experience? In this case I'm not talking about merely mediocre or bad food, but something really off-putting in some way, such as exceptionally bad service, or something amiss with the food, or anything that really makes you angry. Do you simply go away or complain about it, and if you have complained, has it made any difference?