Script a batch file to spawn files with random filenames and then start freaking them out with dir, loop for best effect - cause additional anarchy by duplicating your window (and subsequently, results) to thus cause the staff to congregate.
Cheap trick, good for laughs against some of the library staff who are less knowledgeable to these things, and if you've access to cmd, the things you can do to mess with them are endless, though you may eventually have restrictions placed against you. Also note that the school's jurisdiction may level certain reprimands against you for this activity, so I'd read through their policies to find loopholes or ways to do this without being shouted at.
For pulling these stunts, make sure you sit away from any surveillance and do this from a lab account or a widely-used login (such as a media center's or engineering/lab class's) to minimize the chances of you being caught. Of course, I'm not really encouraging
you to try these things, I'm just throwing it out there.