I would send food back if it wasn't what I ordered or if it was cold or something like that. I never send food back because we don't like it. Maybe some love that sandwich. There was nothing really "wrong" with it other than we didn't like it at all.
For the most part, same here.
We thought the food at BOG dinner wasn't great, IMHO, it wasn't bad, the lamb chops I had were cooked appropriately. Just wasn't tasty and tasted almost like reheated, or speed oven cooked for whatever I spent. My son's meal was fine, Mickey meatloaf, but he was not happy with it at all and wouldn't eat. When the server asked if everything was OK, we said he didn't like it and tried to come up with a substitute, they were nice, and they tried, I forget whether they charged us for 2, I don't think so, I would have been OK either way.
For the Veggie burger, I dont eat those, but if it was completely not what you expected to the point its 1 bite and in the garbage, I'd considered taking it back and state that (nicely) and see what they do as a substitute.
my most frequent take back at a quick service style place is french fries. I can't stand getting them and they're cold. I probably only did it once at disney, but have done it at fast food places by me more frequently.
My feeling is, if its wrong, or not fresh take it back. I worked fast food 25 years ago, but honestly when I was a shift manager, I wasn't pissed if someone brought something back for not being fresh, thats on me, it should be fresh.