The biggest hill here in central Massachusetts is Mt. Wachusett. About 1,000 vertical. Being an hour or so from Boston, it tends to attract a night-skiing crowd that is on the chemically-impaired side.
Anyway, a friend and I went one night when it was C-O-L-D. 5, 10 below or so. They had every snow gun in the place cranking.
At any rate, my buddy and I were inside the lodge warming up and we saw a group boarding the lift in t-shirts. No jackets, bare arms, etc. I'm amazed the lifties even let them on, but they rode up. I wasn't really watching, so I assume they made it back down.. or at least I didn't see them frozen to death out on the slopes when we headed back out.
I don't know how long it takes for frostbite to set in in temperatures like that (I'm guessing "not long"), but that always struck me as being one of the dumber things I've seen on the slopes. I guess if you have enough alcohol / anti-freeze coursing through your veins, you can survive for a few minutes.