The great part is, that when they do open the door to their room, they will think that the prank is that their room is filled with balloons, but little do they know that underneath that an even better prank awaits!
Having to unwrap everything you own is quite a pain but is fun for all the people involved in the setup and wrapping.
Step 1: Gather Supplies
You will have to determine exactly how much of the person being pranked's possessions you would like to cover and make a general assessment on the amount of aluminum foil needed. For a small bedroom, we used 2 rolls of cheap aluminum foil costing about 4 dollars for 200 sq. ft. Reynold's brand aluminum foil will cost you around 7 dollars/200 sq. ft so look around and see if you can find anything at a local dollar store or use a cheaper brand.
Again, take a look at how big the room is that you need to fill. If you're an engineer or a math fiend, you could blow up one balloon, estimate its cubic volume and then extrapolate that to determine how many balloons you will need.
I ended up buying 150 balloons which you will see was just a bit under what was needed in order to fill the entire small bedroom. Plan on spending about 0.15USD per balloon and look for the cheapest balloon with a good size (9-10" balloons work pretty good). Stay away from specialty balloons, you're looking for quantity not quality here.
Pranksters in Training
Invite over a few friends, preferably people who know the prankee and who have a good set of lungs. You'll be spending along time blowing up balloons so the more the merrier and the more maniacal laughs that will occur while staging the prank.
Step 2: Aluminum Wrapping
For ours we decided to try and wrap absolutely everything and do it individually. We wrapped all the pegs in the battleship game that he would play over the phone with his girlfriend and took all the Tylenol and Excedrin pills out of their containers and wrapped them individually. He actually didn't realize that we did that until about a month later when he actually went to use them and several years later they were still encased in aluminum foil as he would only take one out at a time and unwrap it when a headache was coming on.
Also, don't wrap batteries they will heat up and discharge and you could potentially start a fire and at the very least deplete all of their batteries.
Step 3: Balloon Blowing
Pulling on the balloons helps to stretch them out a bit so you can blow them up faster and with a bit less stress but eventually after the first 20 or so you will be able to find a routine and be able to blow them up quickly and to a proper size.
You want to get the balloons as big as possible without popping in your face for two reasons 1) it reduces the amount of balloons you'll have to blow up and tie off and 2) it increases the chance that when the prankee is going through their room that they will pop and make a lot of noise.
Step 4: Waiting and Unveiling
Plan on being home when that person is planning on being home and invite those who assisted to be present as well. If those people cannot be present, set up a camera and record the festivities to show them at a later date.
Don't act too excited when they get home or they will get suspcious of something happening. Let it occur naturally and it will be much better for both their overall suprise and your general satisfaction.
Once they've discovered the state of the room, laugh it up, hopefully they have a good sense of humor as well and will laugh for awhile as well.
Step 5: Cleanup
If you're green friendly, you could perhaps use the foil for another purpose but we just balled it up and made sure we recycled it.
And make sure you take pictures or video so that you can show everyone else the time and effort you put into your prank!