As YouTube user/laser-magician Magx1 says, "it doesn't get much more DIY than this!" After creating all sorts of gas lasers previously, he exhaled his own breath and created a carbon dioxide laser. What did you do with your breath today?
Using nitrogen, hydrogen and helium, Magx1's carbon dioxide laser fires up by breathing into a supply balloon. It's a bit of a complicated set-up, but as Boing Boing points out, you can probably try your hand at building one if you follow the instructions 'round yonder here. [Jarrod Kinsey via YouTube via BoingBoing]