I photoshoped invoices from my university saying that payment was way past due and that the late fines had reached their maximum level and put them in all the mail-boxes in my building.
(I’m relatively new to fluther so this is my best answer)
I didn’t do anything for April Fools(albeit it was my birthday, so I did eat some cake and get presents), but I waited until April 2nd to do all my jokes and pranks! No one expects it on the 2nd!