1. Have a surprise party for someone. Invite many guests. Turn out the lights and Yell “Get Down! He’s here!” After about five minutes say “Sorry. False alarm.” repeat at least 10 times.
2. Secretly take a container of chocolate pudding into the stall in a crowded restroom. Maybe something like a stadium facility. Pour the pudding all over your hands. Matter of factly exit the stall and wash your hands. Don’t make eye contact. (smearing your hands on surfaces or muttering “what a mess” optional).
3. Oldie but goodie. Place a small piece of a Post-It note on the bottom of someone’s computer mouse, covering the ball or optical eye. Job security for the IT department.
Post your best practical jokes in the comments section.
Ooh Something Shiny! 
I did not come up with this but The Amazing Johnathan did. It was you take your video camera and film your bathroom. Mostly the toilet area. Get like ten minuets of film of just the bathroom. Then throw a house party. When someone gets up to go to the bathroom you quick pop the video in and have everyone look at the T.V. and laugh. Keep doing that until the person walks out and enjoy.
Hahaha I tried this one at school.. loooong time ago..
“during your Chemistry Lab session, cover your eyes with your hands and start yelling…’my eyes….my eyes’ .. waste at least 10 minutes covering and yelling.. and remove them and say .. ‘oh they’re still here’ … =p