mouse optical prefered.
a sticky note or not super sticky clear tape.
Step 1: Setup
while the user (victum) is not looking do the following.-
save any open files then you can set up the joke. write April fools on the sticky note or use a sharpie and write it on the tape. flip the mouse over put the sticky note or tape on the bottom covering the lens or the ball. if using a ball mouse tape may work better. flip the mouse back over.
Step 2: Wait
when the user comes back and there mouse will not work. untill the tape or sticky note has ben removed. Scotch tape will realy trick them it is hard to see on an optical mouse and will stop it from working.