It would be, except that it hurts like hell to have a burning jacket on you.
Bah. I spend most of my time inside during the winter, so it's not a big deal. If I go outside, it's between classes, or just very brief. And I can handle extended periods of time. Obviously, I'm not gonna run around in the winter to the point where I'll get hypothermia, and I can stand the cold, so I just wear a t shirt.
That's what happens when I wear a jacket over my Judas Priest shirt.