It wasn't a practical joke but it had me in stitches.
Me and my Mate were fishing a couple of weeks ago, when my swim went dead, I went to where my mate was fishing to see how he was doing.
He had been fishing two rods, one float and one feeder. When I was speaking to him he reeled in his feeder rod and hooked it up to the eye and placed it in the same rod rest as his float rod, which he was fishing with.
His float sailed away out of sight, and to my joy, he struck his feeder rod, I nearly fell in the pool laughing. In the meantime his float rod was in the process of being dragged in, by what turned out to be a 3lb Tench. He managed to grab the rod just in the nick of time. He was swearing and cursing at me to help him, but I was useless, I was just rolling on the floor laughing. What made it funnier was, you know that little glance at the rod tip when you strike? He even done that.
It's just the stupid things that tickle me, and that was pretty stupid, words can't do it justice.