What Is The Best April Fool’s Prank Someone Has Played On You?

I will be the first to admit, I'm easy to prank.  Most of the time I'm in my own little world and I'm not paying attention to what others are doing.  Around here, that's dangerous.When I first started here I didn't have my own phone so I was using a co-workers.  He knew it and one day after I had finished using it I couldn't get it to hang up.  So I'm totally perplexed by this.  I'm thinking I must be the dumbest person on the planet.

I didn't want to tell him for obvious reasons but I did.  He burst out laughing and pointed to the cradle, where I noticed an extremely clear piece of tape holding it down.

That was good, he definitely had me fooled.  What is the best prank some has played on you?