When I was a broadcasting student at a small Idaho college, I made friends with the local radio announcers. One of these friends was on the air, spinning records, and performing his "patter" in between the songs. He included in his comments how hungry he was and how hard it was to work while hungry. It was just natural for me to go by a sandwich shop and pick him up a foot-long sandwich. They wrapped it up in aluminum foil. I brought it to him at the radio studio while it was still warm and set it on the counter where he was working.

"What's that?" he asked.
"You said you were hungry, so I got you a sandwich," I told him.
"I know what day it is today! The last thing you'd bring me on April First is a real sandwich!"
"Okay, I'll take it away."
"No, no! Leave it right there. How do I know it's a sandwich?"
"Well, you open it up and eat it. In fact, you'll want to eat it while it's still warm. What else could it be?"
"I don't know. You could have wrapped up warm clay or something."
"Okay, I'll eat it."
"No, no! Don't take that anywhere!"

We went around like that for almost ten minutes before he gave in, unwrapped his sandwich and ate it.  He was so on guard against being pranked. I completely enjoyed his reaction. So the best April Fool's prank I ever played wasn't a prank at all. It was operating outside of expectations.