I have to tell this story to at least one person a year, and it's almost midnight so I'm just going to tell all of you:
The best April Fools Day prank I've ever pulled was on my dad. It was about ten years ago, and my parents had invited me over to their place to have dinner. After we ate, they sent me on a Dairy Queen run for dessert. My dad loves Dairy Queen. It was pretty much the only place kids had to hang out at in the podunk town he grew up in, so going there always makes him nostalgic. Well, it was April 1st, and the drive thru line was half a block long, so I decided to give him a heart attack. I pulled out my phone and called him...
"Uh, Dad? You're not going to believe this, but DAIRY QUEEN IS ON FIRE!"
He didn't buy it at first. He knew what day it was. Unfortunately for him, his firstborn son is a writer, so I was able to describe the scene in so much detail that he decided I had to have been telling the truth. So by the time I got to the front of the line, I had him believing that the Dairy Queen a couple miles down the road from his house was on fire. He sounded absolutely heartbroken when he told me to just come back to the house. Basking in the glory of my evil mind, I got our ice cream and left.
I got back a few minutes later, but my dad wasn't at the house. I asked where he'd gone, and Mom said that as soon as he'd gotten off the phone with me, he'd hopped in his car and driven down to Dairy Queen to see if there was some way he could help the firemen. We had probably passed each other on my way back.
He got home about ten minutes later. He wasn't happy.
My mom thought it was hilarious.