There is a very funny, though a little bit cruel trick. But are there absolutely innocent jokes?
So, you can play it on your friend, relative, or beloved person- just any one you like.
You can play it in a café, or at home, or even at work if you have dinner with the victim together.

Take a usual salt-cellar. Pour the salt out. Fill it with sugar. That's all!
If you decided to do it at home, you can make the trick more complicated. Make something for breakfast, dinner, or supper, but intentionally add little salt. But don't forget yourself, what the salt-cellar is stuffed with

Wait till the victim reaches for the salt and tries the meal after it and happy April Fools Day to you!