We've always had great tablemates, and on the last cruise, one of our tablemates wanted to play a joke on my brother-in-law. He told our waiter that it was his birthday and had him bring him a cake and, all the waiters came over to sing to him, and the maitre d' even stopped by. I was a little nervous about his doing this at first, because it wasn't really my BIL's birthday, but it turned out to be really funny.
My brother-in-law was quite surprised, and amused.