My favorite office prank was while my boss went out of town, I took all his office furniture, lamps, picture frames, and formed an abstract sculpture with them against the wall. Then I printed out a card like you'd see in a gallery with the name of my sculpture and whatnot and hung it up.

He also had this habit of leaving his glasses on his desk when he left, so I'd sneak in with a dry erase marker and draw funny eyeballs on his lenses.

Gradually built a fake top of door frame, each slightly lower than the previous one.

This guy.

Hmmm, I do like the "make Craig think he's getting taller" idea.

Ooh, like the twits - that's good.

Can you get Joe too?

Giant Joe smash.

Woo! I like this blog. Will it be updated with photos/videos of the pranks?

Let's hide all the t-shirts in the warehouse!

The Prank That Ruined Christmas.

you guys need to prank Regina George. that chick has it comin!

This is why we can't prank Craig. I need his dumb camera.

Three ring binder laptop....solid.

Give Joe a veggie burger. He just might kill a dude.

spray craquehaus with beer.

This is what happens when your mechanic drops off your car and leaves your keys at the front desk...

hahahaha

Prank 1:

Ask Jake if you can see his gray Hoodie during a party... then, give Jake your purple hoodie and a hug and then leave.

Put a lit stick of dynamite in a hotdog bun and then give it to Joe. When he bites into it, it will explode and he will be covered in soot!

well.. everyone loves an upper-decker

Never leave anything with me at the front desk. I can't be trusted(evil laugh).

Alright, I got one. When a co-worker receives a package in the mail, replace the contents with an Evel Knievel jumpsuit ala the picture above. Perfectly fit to their proportions, of course. Who's got a sewing machine and tons of red, white and blue leather?

Prank 2:

Have flowers delivered to a coworker with a card saying they are from Burt Reynolds, xoxo

Fill a box with cement and then some shirts on top of the cement, and tell them to lift it and then when they try to lift it they will not be able to.

You got me, Hippo. Good one.

Something really harmless (yes effective) is bubble-wrap, on the floor, around a corner, preferably in a doorway. You wouldn't believe how little people look down when they're walking.
Changing the location of the wrap is great too, because after someone's been pranked, they'll be looking for it. On the floor just inside a bathroom-stall/urinal is classic, too.

Go to the settings on someone's mouse and change the orientation. Even if they know what's going on it's still funny to see them try and recalibrate it.