With this prank you can crash any PC without causing any real damage.
Step 1: Just Open CMD
The command prompt can be opend by typing "cmd" in the windows search.
(Don't get mad. My computer language is german. That's why it's said "Eingabeaufforderung" and not Command Prompt.)
Step 2: Type the Command "taskkill /IM EXPLORER.EXE /T /F"
With this command the explorer will be terminated.
taskkill /IM EXPLORER.EXE /T /F
Step 3: Tip:
You can repair everything without restarting the PC again. You can do that by opening the Task-Manager (ctrl + alt + rem) and then at the top left you can find "file" and "execute new task" then enter "explorer.exe" and confirm.