Replaced one teacher’s desktop background with a screenshot of the desktop, then hid all the icons and minimized the taskbar.
Got admin access on one of the lab computers to install something needed for a class, and swapped out a bunch of the default Windows sound effects (login etc) with random other sound clips.
Torrented Flatout 2 onto one of the library computers and found out years later a bunch of kids were still playing it during lunch/recess
“Just be a YouTuber/streamer/influencer”