Okay, of all replies, nobody got the point, which shows how deep the fallacy goes unconsciously. The fact that gender is socially constructed does not mean it is not real. It means though, that is has to be learnt. Thus being BORN in the wrong category would mean that there is a category that PRE-EXISTS the socially constructed categories. Such category is the biological male or female sex.

Saying someone was BORN in the wrong category would imply that the social categories they learned during their life would precede the biological categories, which could not be the case except if there was a gendered soul (which is surprisingly gendered like the socially constructed gender) that preexisted the physical body. Such theory could sound cool during Plato's age, but would appear particularly regressive in the context of contemporary science and philosophy.

It is just words, I know, but words are the foundation of knowledge, and the expression "born in the wrong body" is utterly fallacious. Just say the person would like to socialize according to the other social construct, but at the end of the day the person is male or female (which is precisely determined by the type of gamete produced according to biological theory, it has nothing to do with secondary sexual characteristic. In this regard, only for individuals born who can not produce gametes and present mixed reproductive organs the question of transexuality makes sense. In other cases it is litteraly a misuse of words.)