OMG the people who do this... And since you're on the business side of the counter, you can't always call them out on how absolutely inappropriate and rude that is.
I got this crap all the time when I was in school and working, and I still get it now occasionally with the added bonus of the rude customer implying that I guess I shouldn't have gotten such a worthless degree. Ha ha ha.
And then they wonder why the customer washroom is always "Out of Order" when they ask for the key, or why they can never get an extra twenty changed while the till is open, or a hold on items they want to buy the next day.
It's because people remember when someone is an asshole, and they treat them accordingly.