Interesting ! Is that a worldwide special day ? Does it also exist in let's say China ?
Unfortunately I made a paper fish (a fish with the shapes of the girl I would like to fool) to stick it on the back of her coat, but in the end I forgot. Jokes with "fishes" are probably way too classical to be original, I know. But it was almost noon when I realised it was April the first.
In yesterday newspaper I read some interesting jokes from the past.
A BBC-joke from the fifties "that the harvest of the spaghetti-tree was very good this year in Switzerland ! There grew exceptionally much spaghetti on the trees this year, with a visual proof and all (black and white footage of a lady with a sjawl over her head that touches some white long (what's the name for that in English 'one cooked piece of spaghetti (in Dutch it is "sliert") hanging from some kind of a tree ! People called the BBC that year, to ask how to grow such trees...
There was a nice one in America too 'the left-hand Burger' - a kind of Macdonald's Big Mac, with the greens (salad, tomatoes, onions) organised counterclockwise

on the burger. People were actually especially asking for that Burger for lefthanded people...
Kind greetings.