Hmm -- see if you can do it in three minutes. Bring just a wheel, not the whole bike.

Besides that, I might avoid the obvious stuff (road bike racing, radical MTB'ing, X-Games-like BMX) and do a Commuter Bike presentation. If you don't have a fully-equipped commuter rig, go to Koga's build-a-bike page and grab some screenshots to use for a quick Powerpoint/Keynote presentation.

I did a presentation on how to lubricate the valves on my tuba. Some of the kids thought it was fun, and the professor appreciated the extra knowledge I passed along.