Have you ever refused a mandated tip as part of a group?

I have a cousin who invited a group of friends and relatives to a group, each guest going dutch. At the end, the waiter announced that an 18% gratuity has been added to the bill. If it wasn’t part of a large group, I would have disputed it. But, they kinda gotcha when it is obvious that ppl don’t want to contest this in front of others. Even if he had said it at the beginning, it is still embarrassing to leave the function even if I wanted to. The entitlement of these servers is on another level.