What are your favorite real-world April Fools pranks (not that online 'toilet internet' stuff)?

When I worked as a systems admin, my office had those motivational posters all over the place so the night before I went through the entire office and replaced them all with demotivational posters.

It took almost 6 months for anyone to notice, and it happened to be a foreman from the mill that was bored waiting for the accountants to fix a payroll issue or something. My boss fucking loved it though and asked me to keep them up.

I am the unofficial pastry Chef at my restaurant (because I am the only one that knows how). Whenever I make crème brûlée I normally make a couple of smaller ones for me and the BOH boys to snack on. The servers like to sneak into our walk in and steal them from where I stash them for my guys. If we were open today I was planning on filling some ramekins with mayonnaise, bruleing them and setting them in the walk in "for the BOH guys" and then just waiting.

Not so much April Fools specifically, but something that happened at my school before everything shut down. About two months after school started, these little blue stickers started to appear around the campus. They had a crude drawing of a pair of pants (I think), along with the words "For Rectal Use ONLY." Whoever had these stickers were just slapping them around on any vaguely phallic-shaped object: door handles, fence posts, sinks, water fountains, etc. Coincidentally, the administration decided to spend $50,000 on replacing the decade-old security camera system last month