Geez, this is really inspiring me today. Here's another good idea I've seen in large scale, but not yet in small.
Write a song, in the style of a stage musical. Make sure it has a verse for each of at least five different vocalists. The song can be about anything pertinent to the setting, such as the tragedy of a broken pencil, the discomfort of a chair, or the stress of a test.
At a preset time during class (extra, extra points if done during a test; the quieter the setting before, the greater the effect during), start playing music. Launch into song, and ham it right up. Then, when your verse is complete, have a friend or acquaintance suddenly stand and burst into the second. And so on, and so forth, until the song has played out.
If you want to see this in action, check out this improv group's spin on it, performed in a mall food court:
http://www.youtube.com/watch?v=dkYZ6rbPU2M
The same group did a truly grand-scale version of your freezing trick, too:
http://www.youtube.com/watch?v=jwMj3PJDxuo&feature=channel
These experiments are amazing to watch.