Probably not too bad - at least for such a high-powered laser. Most materials absorb the CO2 wavelength, and won't reflect the beam. However -and a big HOWEVER - if the beam does hit something reflective to that wavelength, like many metals, imagine what a hit from that kind of laser power would do to your flesh - especially your eyeballs!
I don't know if the guys in the vid had goggles, but personally I never operate mine unless I have my goggles on.
The lens of the eye does not 'pass' 10,600nm light, therefore a CO2 laser cant do any retinal damage. The danger with a CO2 laser is burning the outer surface of your eye, because it isn't 'clear' to the laser, it will cook it. Basically like staring at the sun but without retinal damage. Instant burn of the cornea
