completely freeze a can
of shaving cream. I usually put it into the freezer for at
least two days to be safe. Now cut the can in half with a
hack saw and place the frozen contents in the victims car,
dorm, office, etc. As the shaving cream unthaws it will
expand to fill a car or a small room. This is a really mean
prank so be careful who you do it to. However I've had much
amusement doing this to my friend's car while he was dining
with his girl friend. It is also great for portable bathrooms.