Me, I don't look at cost so much as value recieved. With that in mind, I'm curious what your worst restaurant experiences were. Or maybe we should just call it worst dining out experiences?
For me, no contest, it was the five days spent as a prisoner on a Holland-America cruise ship. I didn't get a hot meal one night; which, apparently, didn't matter much as the food, overall, was no great shakes based on what other people had to say.
And, of course, nobody on the food service end speaks English, so you can't even find out who to complain to.