While it definitely lacks the low-budget charm of this nearly identical classroom presentation, this demonstration of liquid nitrogen's explosive potential does have two major things going for it. One: more ping pong balls. Two: A high-speed camera, for slowmo playback goodness.
Come for the science, stay for the explosions. Watch Plymouth University professor Roy Lowry* demonstrate what happens when you try to contain liquid nitrogen while it's returning to its gaseous state. (The impatient among you can skip to 3:15.)