Hubby and I met at work about 6 years ago. We worked for a civil engineering firm, so our day-to-day work was done on the computer. One day I go to open the program to work on a project and the entire software program was upside down!
Hubby implanted some programming text that made the program appear upside down on the screen. He sat around the corner and just busted up laughing as soon as he heard me mumble "What the heck?!?!". Luckily he came and fixed it immediately.
Another one that he did was tape down the hang up button on the phone on my desk. So, when I went to answer one of my phone calls, I pick it up, but my phone was still ringing.
And yet another one.... (April Fool's is an interesting day with my DH)
He tied a rubberband around the sprayer on our sink, so when I turned the water on in our kitchen sink the spray nozzle went off and my shirt was soaked!
Oh..this one didn't involve my DH...he's not this mean...
The guys in the office all knew that the secretary was scared of bugs. They collected a few dead roaches and put them on her desk and placed a piece of paper over it. They told her they needed a copy of the paper (or something similar to that) and when she lifted it she gave a nice, blood curdling scream! She was ticked for better part of a day.