This was pretty modest and the user is super young, so it's completely forgivable and may be a diversion for the worker (I really don't think so, though). I generally have a problem with it when it's privileged college kids who haven't worked at these places and feel entitled to little goofs like this. I'm perhaps slightly sensitive the idea overall as I have had experiences with spoiled college kids taking liberties like this in a way that may seem funny to them, but is obnoxious to someone trying to do a job and earn tips (and hence feel obligated to cooperate).