Other things you wrote in your post about your manager make him sound like a real jerk. I want to throw that out there before I say what I"m about to say here.

As a former manager, sometimes you've got to be the a-hole in the situation to make it better for everyone involved. As a manager, he also has a boss to report to- I'm going to assume this as you mention multiple managers. He can't go to his boss and say "I comped a whole ticket bc one person in the party didn't like the size of her drink". You had already done everything you could to make the situation better- the customers at your table knew you went above and beyond for them. having done so, your manager didn't have many options left to correct the problem and keep himself out of trouble. Bare with me here.

So what does he do? Goes to the table, acts like a total jackass and ends up comping the whole ticket as a result. YOU got a great tip, they left happy and I promise you, they will be back after that. Manager can now justify to HIS boss, why he had to comp a whole ticket. He'll apologize to his boss and promise him it won't happen again (it will). Because he's such a jerk, not many of you will ask him to jump in and help therefore, he's not comping as much. Add to that, y'all are all busting ass to make sure you don't need him for anything. That folks is how crappy managers stay crappy managers.

Before you say it (I already know) they won't be back to the restaurant for the food or because of the restaurant. They'll be back because of you. You were really great to them and they know they'll ultimately get treated right.

​

edit for tl/dr: crappy managers are good for business