The only time that I would take my shirt off growing up was if I was doing something involving water, swimming for example. I did feel pretty uncomfortable doing so, idk maybe even felt kinda wrong doing it, so right after I was done and usually somewhat dry at least, I would put it back on.
I had mostly guy friends growing up and I know that they would do it if they were playing sports or just hot even. Always seemed weird to me.
I stopped doing it totally when I first decided to start trying hrt (herbals, before I had ANY trans knowledge at all..). I was totally skinny and totally flat, hardly any muscle there even, but to me, it was like, I started on this journey and instantly my mindset changed to its now inappropriate for me to go topless.