I feel it's cold, but it's not uncomfortable or painful for me. I'm doing this daily since hmm 10 or more years - walking in shorts, t-shirt, almost all year long (something longer if it's cold, cold meaning less than -15C or less than -3C and extremely windy). Similar story with rain - just get wet, it's fine. Hiking, running in one layer instead of 3 layers as most folks would do... It helps me with overheating which I tend to a lot. I have also a simple recipe if I'm actually feeling cold - just do whatever you do faster (your muscles generate a lot of heat as a by-product), no need for extra layers. Lately I also monitor my core body temperature when doing any kind of activities - definitely not getting cold inside even though I'm "underdressed" by popular opinion. (Note I'm also not a risk taker, so in extreme conditions I always have some backup layers with me, in case "do whatever you do faster" method could not be implemented anymore).
I wouldn't give anyone any advice out of this though, I'm not a medical professional.