Sure, I'll bite.

All of these people are wearing what we might consider skirts or dresses and yet some of them are men.

Little boys also used to wear dresses as a matter of course.)

Pink used to be considered a strongly masculine color. Fashions change, and are often designed for either men or women as a way of highlighting their secondary sexual characteristics or whatever are culturally seen as desirable features, in essence advertising sexual maturity and fertility (and wealth and whatever else might be useful to draw a mate).

Sex is categorical and immutable.

Everybody with a y chromosome is male. Everybody without a y chromosome is female. No matter how many surgeries they have or hormones they take, a man can not change the fact that the egg (from a female and only ever from a female, by definition) that spawned him was fertilized by a sperm (from a male and only ever from a male, by definition) bearing a Y chromosome instead of an X. He will never be of the female sex no matter what clothes or makeup he wears. By the traditional definition, he will never be a woman, because "woman" is the word for an adult human being of the female sex. "Man" is traditionally the word for an adult human being of the male sex. That's why trans people are called "trans", because they are, by definition, not the thing they aspire to be.

A man who dresses in the current cultural stereotypes of women's clothing and performs current cultural stereotypes of behavior ascribed to or imposed upon women, and legally changes his name and all his documentation, and even "passes" as a woman, is still a man by the traditional definition. Just like a cake that's decorated to look like a hamburger is still a cake, and when you bite into it, you know you're eating sugar and flour and not beef. You would still call it a cake, or a cake that looks like a burger. If it was really well done, you might even call it a burger until you got up close enough to smell it and feel it, and get a good close look at it. And of course as soon as you cut it, you would know it was definitely not a burger, but some kind of cake. And there is plenty of room in the world for cakes that are splendidly decorated to look like burgers, but they are still cake. Because the word for that baked-good is "cake" and the word for that ground beef patty is "burger".

Plenty of languages have grammatical gender such that certain words are arbitrarily considered "masculine", "feminine", "neuter", or other things. For example "pen" in French is masculine, while in Russian, "pen" is feminine. In Arabic it is also masculine but the plural "pens" would be treated grammatically as feminine singular. In ancient Greek at least, all children are neuter. In Dyirbal all animate things are masculine and all dangerous things are feminine. Natural language grammars are peculiar and not really relevant to your argument, and bringing it up is trying to muddy the water, just like muddying the distinction between culturally-determined societal gender (a co-opting of the term from grammar) and sex. English has not marked inanimate things for gender in several centuries, and the long-standing modern usage of pronouns is that things of the male sex (boys, men, bulls, roosters, stags, etc) are conventionally referred to with the masculine pronoun "he"; and things of the female sex (girls, women, cows, hens, does, etc.) are referred to with the feminine pronoun "she"; and inanimate, indeterminate, or sexless things (pen, table) are called "it". In sum, in the English language the gender of pronoun used is determined by the sex of the referent.

Most people – including most transgender people – are either male or female.

All people -- including all transgender people -- are exactly one of male or female. There is nothing else.

You are aware that plenty of plants and trees and all sorts of animals are also sexed? As in, they reproduce sexually? Sex class determination is based purely upon the reproductive mechanism. That is the definition. The peacock with the big decorative tail is the male, even though we stereotypically think of human women as the decorative baubles who strut around making a display for sexual attention. The peacock with the big decorative tail however is not the female just because he looks pretty; he is the male because he has the sperm and the plain brown peahen is the female because she has the eggs. Whatever other cultural baggage and stereotypes we might hang on someone or something does not change the definition of their sex.

I am hoping that you are just young and not that you have been let down by a terrible education that failed to impart to you that there are objective facts in reality and that many concepts are defined based on objective facts and not illusions and feelings. The color red is not a nebulous philosophical concept that differs from person to person, it is defined as a specific wavelength of the electromagnetic spectrum, and how you subjectively perceive and experience it is immaterial. Similarly, a man who wraps himself up in all the trappings of womanhood, and surgically or otherwise alters his secondary sexual characteristics to make him seem more womanly, cannot negate his primary ones.

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