What’s the best, funniest, and most successful prank you’ve pulled on someone?

  Too many to choose from, so I'll have to go for memorable and funny rather than decidedly best. 

  I was stationed in the Pacific at a base on an island that had a lot of wildlife. After going on patrol in the jungle one day, my platoon was returning to when I spotted an old discarded leather satchel that looked as if it had been there for years. World War II battles had been fought there, and decades later, artifacts were still being found, so I picked it up. It was very old and weathered, had no markings on it, but I couldn't tell if it was 1940s vintage. Also, it turned out that there were no artifacts in it. I kept it anyway, and minutes later, we marched into camp.
  Another platoon was staging near the gate, its sergeant was a guy from Tennessee, and for some reason, I suddenly thought I'd pull a trick on him. Acting all excited, I yelled out to him, "Look what I just found, I can't believe it has all this money in it, I'll bet it's a collector's item!"  As soon as I said the magic word, money, he came running. He poked his big mitt inside the bag and pulled out the fake rubber snake that I neglected to disclose above. Thinking it was a real live snake, his eyes bugged out as he dropped the wiggling toy and he jumped nearly five feet in the air straight up. He took of running, did a 100-yard dash, and both platoons were bent over laughing.  "Where are you going?" I shouted after him, "It's only a rubber toy!" When he realized he had been had, he cursed me out a blue streak. As it turns out, he had been deathly afraid of snakes all his life, and on patrol his biggest phobia was encountering one in the tropical setting in which we were stationed. The men in his platoon knew that, I didn't.
  Eventually, he cooled down, but for the rest of the deployment, I had to watch my back for the day he'd seek revenge. (He never did.)

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