In this short experiment I show you how to make a ring pattern using only a laser and a fingerprint on a mirror. The ring pattern only emerges due to interference, which only happens in waves.
I highly recommend you give this a try yourself, I find it very easy to do and the result is pretty impressive I think. The darker the room, the more impressive the result, so I recommend doing it at night with the lights turned off.

I reiterate that you should use a laser from a reputable source. Cheap lasers from china, and those lasers resold by vendors on ebay, amazon or bol.com, are often more powerful than what it says on the label, and that can cause damage to your eyes. This is even more likely if the laser is green, blue or violet. Because of the geometry of this experiment the laser passes quite close to your head.