I pulled an elaborate joke on my admin troop when I was in the USAF. I ran a school for aircraft maintenance people and could have around 100 students at one time. I had various people call the office looking for Captain Smith. I made sure that we didn't have a Captain Smith in a class. The first time Bob went through all the class rosters looking for Captain Smith. After the second call, he looked again. About the fourth call, he started asking each instructor if they had a Captain Smith in a class. About the 10th call, he was checking with the base locator roster. I hadn't thought of that, but luckily there wasn't a Captain Smith.
Towards the end of the day, and about 20 phone calls, I had someone call Bob and say "This is Captain Smith. Did anyone call for me?" Bob was so apoplectic that he couldn't form any words. That's when the whole office burst out laughing. Bob should have known something was up as almost everyone was crowding around the office at quitting time.