That's a great story. Last place I worked had a few pranksters too, me included. One I did was taping a fresh urinal cake to the bottom of the lead tech's chair. I barely tore open the plastic packaging and it reeked so bad I had to put extra layers of packing tape over it to keep the smell to a minimum and finally got it to where you could only smell it if you were sitting it the chair.

I quietly watched his reactions. He'd sit down and get an odd look on his face, sniff a bit then go to work, sniff a little more every once in a while and once every so often look around and in the trash can for whatever was causing that smell. A couple of weeks went by and I finally thought I better go back there and tell him before he turned green and got real sick or something. I rounded the corner to his desk and he had just flipped his chair over, looked up at me red-faced and yelled, "Who the fuck did this!?!?" I was laughing so hard I couldn't speak and just raised my hand. I thought he was gonna be really pissed off but he thought it was funny as hell and laughed about how he'd been looking all over for the source of the smell and was ready to tear his whole desk apart when he realized it came from the chair.