"Picturing"

This is a great prank for college or high school students.

When the person walks in to his room, it is covered with hundreds of pictures of a girl he has liked "secretly".

Be ready with the camera, because the pictures of him being surrounded by hundreds of pictures of her will be priceless!

Supply List
1-2 rolls of scotch tape
hundreds of photocopied (or for flair with those of you with lots of $) color printed pictures of a particular girl. (The girl picked is key in this prank.)

Plan
Take your supplies and enter the room and lock it. Quickly go to work. You will need multiple people if your time is short.
The plan is to entirely cover every inch of the room. Start with hanging dozens of photos from the ceiling. Cover all of the walls, all of the furniture, you can even cover the entire floor. I personally would leave the outside of the door alone to add to the surprize factor, but covering the inside of all of the drawers and putting photos in all of his books is a nice touch as well.
For bonus points make large prints for the windows (make sure the picture if facing out.)

A web cam set up in the room facing the door and his look would also make a nice addition.

Cost saving tip
Make the photo copies at the computer lab. If there are photo limits, get 4-5 friends each to max their daily limit for a week or two. That should get you more than enough photos.