I love April Fool's Day. It gets harder and harder to pull off a good April Fool's joke, and it's a thin line between hilarity, cruelty and just plain mean.
Hilarity: if you're in a sugar daddy/sugar mommy relationship, and you are the previously mentioned sugar daddy/mommy, tell the freeloader you have an itemized list of your gifts to them and need them to start paying you back with interest for each and every gift that took you over the Federal gift tax cap of $12,000/year. Drag it out and see how many awkward facial expressions they make.
Cruelty: Call all your exes and inform them that you have herpes, but you're on Valtrex, and you didn't think you were having an outbreak when you hooked up in the past but there's really no way to know. Also tell them it's really not so bad, you've found plenty of other herpes singles to date since finding out you had it.
Mean: Tell your friends you are dying, and Make-a-Wish foundation does not make wishes come true for adults. I have no idea if that's true or not. Regardless, see how many free drinks you can squeeze out while you commiserate over the "time you have left."
I haven't played a lot of April Fool's Day jokes recently. In my first pass through undergrad when I was living in a dorm and had a roommate (this was before everyone used their cell phone as an alarm), I set his alarm clock ahead two hours so he would panic when he "overslept" for classes, and oops he actually had a court date... he was pretty pissed but we laughed about it later. :)