My legs generally don't get cold. Even in that -20 C weather my legs just don't seem to be bothered. I have no idea why, other than I'm acclimatized to cold weather or something, though it's possible there's some nerve issue in my legs that makes me not feel the cold - again, no idea.

Other parts of my body get cold, like you won't catch my shirtless or shoeless in that weather.

On the other hand, if I wear pants, my legs will sweat profusely and get itchy, which is way more uncomfortable to me. I'm also generally a very warm person, and usually sleep at night without a blanket covering me (otherwise I'll sweat all night and be uncomfortable). If I turn the thermostat down then blankets become tolerable, but then everyone else in my house will complain it's too cold.

I'm also aware of the dangers of frostbite, so if I expect to be in -20 C weather for extended periods of time (like an hour or two) then I'll put on pants. If it drops to -30 C then I always put on pants no matter how long I plan to be outside.

Hopefully this clears up some of the confusion, though I expect it also raises new ones.