I have never done this before. But last night I did have occasion to refuse a red snapper dish as the fish was past it's prime. I asked for it to be removed from the bill. They said they ould only discount 15% because some of it had been consumed. I had one bite, brother had two bites and it was deemed icky at that point. OK, now how are you supposed to evaluate a dish unless you taste it? When discussing the "discount", waitress says that they are eating the same fish (was it ours?) in the back and it was fine. Was I unreasonable in wanting the whole dish comped?