How old are you?

We took some friends out for dinner a while back. there were 7 of us total. I pulled the server off to the side and tole her that it was a special occasion and I'd really appreciate it if she could be "Johnny on the Spot" when taking care of our table. I TRIED to explain the phase to her, but I wound up just saying, "If you could take extra good care of us tonight, your tip will reflect that" I probably should have known better.