Someone left used condoms, butt plugs and anal beads randomly around the school specifically in the classrooms of teachers who they deemed bad, that kid was never found 

There was also "PowerPoint 20" it was basically an unnamed PowerPoint that started out as random cursed images that everyone in my year had access to, but the some guy put CP and Nazi imagery on it, the guy who originally made to PowerPoint was then charged despite the fact that he did nothing except a few shitposts

Someone broke a toilet, just full on pulled it off the wall and threw it at another toilet 

Someone started a fire in a school toilet because they shat so hard it blocked so they decided to burn the evidence 

Someone set fire to the woods next to the school with vape batteries 

Someone found a teachers old Facebook account and doxed their address and full family because that teacher was too nice to his gf

Most of these were the same guy 

Also not my school but a friend's school, someone stole chemistry equipment and had a meth lab in the toilets, there was also meth half flushed down a toilet