In my early 20's, I was in the kitchen and my mother asked me to turn around. Then she ran her fingers through the back of my hair and said, "You've got quite the large bald spot going there!"
I raced over to the hallway mirror and frantically tried to check the bald spot when Mom laughed and yelled from the kitchen, "April Fool's!"
Mom really got me that day. She never played tricks on us, so it was quite the surprise when she pulled this stunt on me. I still remember it over 35 years later...yes, it was that good of a gag!
Arguably the best April Fool gag ever had to be the BBC's: "Harvesting Spaghetti." A short film showing spaghetti growing on trees and being harvested by farm workers. The presenter, a doyen of the BBC, Richard Dimbleby, gave it gravitas with his serious facial expression.
To this day it has to be one of the funniest jokes ever.