I've only ever sent back food if it's improperly cooked or the wrong order, and most times people have been pretty civil about it.
I've also seen someone verbally destroy a waiter. Their father asked for a Diet Coke, they received a regular Coke. His father was diabetic. They returned the Coke, and replaced it with ANOTHER regular Coke, possibly even in the same one. Cue the world's most angry son:
"Does my father look fat to you? Does he look like he's trying to lose weight? Did you think it wouldn't matter? Did you even think at all? My father's almost lost his foot because of stupid, understandable mistakes - you made a fucking stupid, lazy, mistake!"
The waiter looked pretty meek after that.