A co-worker and I often ate lunch with our administrator. She was a fiesty lady. One day right before lunch she came to us and said that someone had been using her salad dressing in the refridgerator in the lunch room and that she was going to put a label with her name on it, hopefully to deter anyone from using it without permission.

Well, a few days had gone by and she came to us again, frustrated and a little angry that her salad dressing was still being used. So the next day, me and my co-worker thought it would be funny to play a little joke on her. Although we didn't know who was taking her dressing, we wrote a little sticky note that said "You are getting low, can you please buy more". We stuck it on her bottle of dressing and put it in the fridge.
An hour later, the administrator stormed into the office holding her dressing bottle and couldn't believe the nerve of this person!
Later that day we let her in our little joke. I still laugh to this day thinking of it!