Ahh... I love ya, J..
But I think you are veering off a bit with the restaurant thing. Many folks mentioned taking the bad grapes back to the store. It is essentially the same as sending back the food at the restaurant, except at the restaurant, you are also paying for value added due to the preparation aspect. And as with my response to the other, I think it is a matter of conscience. I am not someone to go into a restaurant and make a big stink over a side dish being cooked less than perfectly. But if I am paying $20 for a steak that is MR and they bring it to me well done, then I am sending it back. They messed it up. I honestly have never had a steak served to me that was tough. But then, I almost always order a filet, not other cuts.
If my kid just doesn't like their food, too bad. They'll learn to make a different choice next time. If the meat is bad (I tasted it and it tastes like you said--the meat was bad before it was cooked or whatever) then I would say something. Partly, because I would want the restaurant to be aware so they don't serve it to someone else and have a lot of people getting sick. And partly b/c I want my kid to eat without getting sick.
I have been to places that I thought were way overpriced for the food/service, the food was less than great, though not spoiled, and I smiled, paid the bill and left. And never went back again.
Back to the grapes, though... you are assuming that grape is bad. What if it was a good grape?
But anyway, the store I shop at, the grapes are not sold loose. They are in clear ziptop bags. So the bag catches anything that falls off the bunch. :)
And if the bagboy stomps on one that did fall out of the bag (I tie the tops of mine in knots, but... just say one fell out)... then that is on HIS conscience. Not mine. And of course I wouldn't make a scene about it, but technically, I could, since the grapes were paid for and belonged to me. I'm sure the store would compensate somehow, but who wants to go through the hassle?
What I DO get annoyed by, is when you are very careful choosing unbruised apples, and the clerk/bagboy just tosses them around on the metal checkout area with no concern that they cost $2.29/lb and you don't like them bruised. And yes, I have spoken up about that in the past.