Chaotic Good

Stick a piece of tape on the bottom of laser mice. It stops them from being able to detect motion.

Screenshot your buddies desktop, then save that image to the desktop. Set it as the desktop background. Now right click, select "view" i think, and click "show desktop icons". In theory, nothing should noticably change. But now you can no longer actually click on the icons on the desktop. To take it further, open task manager. Find "explorer.exe" and kill it. Now, you cant even right click to reshow desktop icons.

Easy fix to that is to reboot the computer, but you can also just reopen task manager, start a new process "explorer.exe", and then reshow desktop icons.

You can find a website that has fake versions of windows update screens. Load one of those, hit f11 to fullscreen your page, and enjoy as your friend waits for three hours at a bar that has only gone up 2%.

Open task scheduler. Add a new task. Set it to run every day at like 2 pm. Have it set volume to 3/4, then open firefox with the extra command "https://www.youtube.com/watch/dQw...." and you will have a great time.

For a more malicious prank, get a syringe. Fill it with raw egg. Inject this into the seats of some assholes car. Within two days, their car is not able to be sat in without the windows down, and even then it is horrible. They cannot figure out where the smell is coming from, and even if they do, they have to replace the seat. Optionally you can just throw a dead fish into their gutter, they wont find it for a couple days at least, and it will permanantly make their entire yard smell.