I'm often cold when other people aren't. In the 80s and 90s, I'll be happy and comfy, and everyone else will want to kill me because I'm bouncing. Doesn't matter how thin or fat I am. Hydration does matter, because I lose a lot of heat tolerance when dehydrated. If I feel cold, I put on a sweater or a hat. If I feel hot, I drink more water or put on a hat. Hats are lovely things for temperature control.

So I tend to figure I'm just an oddball who likes to be a bit warmer than average. It doesn't take much forethought for me to be comfortable and stay comfortable.

It's not unusual for people to be sensitive to cold *and* sensitive to heat. If it's not causing serious trouble (and no, packing a light jacket in the summer doesn't count as serious trouble), I wouldn't worry about it. If it's to the point where things like layering, wearing a hat, and drinking plenty of fluids don't solve things, you may have a problem. If you've got a history of hypothermia or hyperthermia, then you've got an easy explanation. Once you've had some form of trouble with your internal thermostat, it's much easier to have trouble again. Lots of other possible medical explanations, but very often it is just your body doesn't take extremes well.