For april fools' day, on my first job as a troublesome ~16-year-old administering our university lab's firewall (academia was a different land when it comes to trust), I set up some automatic network-wide substring replacement filters for incoming HTTP responses to replace `<body` with something like `<body style="transform: rotate(0.1deg);"`. This was in the time before HTTPS was ubiquitous, so it worked on most websites.

Unfortunately, it broke some pages that lab users needed for school. I later learned one colleague wasn't able to complete a homework assignment because of my prank.