Ummm, not to get anyone into trouble, there is much you can do to a car without damage to the paint or exterior.
First you obtain some soft dish soap, I recommend Dawn as it cuts grease, and could help to clean the car in the end.
Spread the soap a little on the car, this helps to hold the toilet paper in place. You need some of it to not stick and flap for best visual.
THen if you really are mean or getting even, get some industrial shrink wrap. Most shipping docks will have this, or a furnature store, and wrap the car in the evening hours. When the sun comes up and hits the wrap it will shrink to the car. This in itself does not damage the car. yet depending upon how much you put on, you may need to cut it, so do not put to much on it.
If your vehicle has been such treated, and you get the plastic off of it then you can go to one of the drive in quarter car washes and the soap has already be supplied for you .
Remember you should not damage other peoples property.
Yes we did have way too much fun doing this...you should have saw the cars that almost hit yours and the others from looking at it. they may have been blinded by the reflextion too....now we aren't that evil. we stuck around and helped take the tin foil off. and the nice thing about tinfoil is it didn't mess the car up but we did have to go to the post office to borrow their tape. Evil blah, it was fun and you asked for it.
Your reaction was different than what we thought...we thought you'd hit us soon as you caught sight of it...or at least i did...but you hit me anyway...