If you’re saying boobs are just fat around someone’s chest, fire away.

I'm saying boobs are breast tissue. I'm fine using a definition that doesn't consider fake boobs as boobs. There is a literal different type of tissue in breasts and some men have a lot of it, even more than many women. Men who have a lot of breast tissue are susceptible to getting breast cancer.

Boobs are on females.

How about lets not use a definition like requires defining gender first since you're opening yourself up to circular reasoning. Fine, you don't like boobs? Let's say significant amounts of breast tissue. Some men are born with it, most aren't. Some men get more of it through hormone treatments.

By taking hormones you will literally change the things about you that define your sex.

Your genitalia are completely determined by hormones, not that they can be THAT changed later in life. But still if your body gives you female hormones from the time you were a fetus, you would have a vagina and boobs and everything else, even if you have XY chromosomes. We know this because some people have that exact issue.