What are some great, easy pranks on some guy-friends?

If they have cars then this one is gold . This one would also be best done at the school parking lot - if possible . It's simple : all you do is remove two of their hubcaps - one from either side of the car - and place a small rock or two inside . Replace the hubcap and be on your way...and be there when they do drive off.It will cause no damage at all but when the wheels start to move it will clang and bang in an embarrasing manner - and they won't know what it is. Once they DO figure it out then they have to go through the hle of removing ALL of their rims to find out if there are any others . It's gold - especially if you can do it on the same day to more than one of your friends.