I'd disagree. If it was one of the professional paintball guns (not the plastic-crap ones) you're talking 50 caliber in size, and muzzle velocity approaching that of a 45 caliber handgun.
I didn't know they traveled that fast. I think that would sting some! Seriously though, I've seen film of people doing that and they always have eye/face protection on. At the least, it should certainly leave a nice welt on unprotected skin.