Sheesh. Where would I start. So many awesome ones over the years.

For or you office type folks, punch someone's chair in under their desk, tie some fishing line to the bottom of the chair and bring it up the other side of the desk and tie it everything on the top of the desk (stapler, phone, file rack type things, etc.) then wait for them to pull the chair out and watch everything go flying off the back side of the desk.

One of my favorite pranks is to put a rubber band around the spray nozzle thing on a kitchen or brake room sink and make sure it is pointed to where whoever turns the faucet on will get hosed.

Of course most of my pranks have been automotive related. Had a 140 decibel mini siren we would stick up under the dash and wire to things like window switches, turn signals, etc. Blowing up antifreeze jugs with compressed air is always entertaining if done in an appropriate time and place.