I'm not sure what practical means. I'll look it up later.

Here's a fun practical joke you can pull on your friend. You'll only need a few basic household materials: a rubber band, 3 paper clips, a ruler, and a marble or some kind of clay.

Here's what you do:

Wait till he's not looking, then make sweet, tender love to his girlfriend.

You can do whatever you want with the other things. I usually just throw them away. Come to think of it, you can probably just skip to step 2.