My favorite prank was about 15 years ago. One day at work, a guy in the office came back from Subway to eat his sandwich at his desk and he told me when he was getting his drink that he spilled all of it on a guy standing next to him. He said, "I looked at him for a moment and then just ran out of there!" I just looked at him and said, "Really? You didn't apologize? You turned and ran? You are 45 years old! By now you should know how to say you are sorry when you cause an accident." He was not apologetic at all and kinda laughing about it.
So, me being me, I went directly to the receptionist and told her to call his extension and tell him some guy was on the phone saying that he just met him at Subway and wanted to talk to him. I went back to my desk and observed his reaction when Janice came on his intercom and told him. He came out of his seat and sat right back down. He checked his back pocket for his wallet. He looked like he was ready to pass out in fear. He took a deep breath and picked up the line. "Hello, this is John. Hello? Hello?" He hung up and called Janice. "Where is he?" She played dumb. "He's on the line, John." He composed himself and tried again. "Hello, this is John." By now he was sweating. Profusely.
I alternated between shaking my head and laughing. He called Janice again. She told him, "He's there John, pick it up." He responded and his voice was an octave higher than normal. I really started laughing and he turned to me and realization dawned. "STACEY!!!!" I said, "That's what you get, John, when you don't take responsibility for your actions."
My best prank ever.