One of my favorites is walking around w/ a 2048 C tuning fork. That is one that rings uber high-pitched. I'll walk around w/ ti ringing just to see how many strange and/or dirty looks I can get. What's real fun is if you can hide the fork then you strike it and start looking around as if you were trying to find the source of that blasted ringing is coming from. I strongly caution all NOT to do this if you cannot keep a straight face. If you start to smile everyone who's paying attention will know it is you and you will get yelled at. HS students: your teachers will go nuts and your classmates reactions will likely be priceless. College students: do this in the hallways and lecture halls. Watch for people's reactions. Everyone else, well, just enjoy. Movie theaters are fun places to do this in.