When they say femboy they mean that they are a trans man that doesn't present itself as manly enough or a trans female that hasn't transitioned that much yet?
In one of those cases being into dudes would be being straight.
No, a femboy is a feminine boy. They usually crossdress or at least dress androginously. They don't necessarily want to transition or take HRT (although this one does).
Given that this one does, and that a trans person that wants to transition would refer to themselves as the gender they want to transition, they would be a trans male. However it's 4chan and fake so I bet they meant a trans female, where being into dudes would be being straight.
He can still be an amab femboy and take hrt to become more feminine without transitioning to become a woman. He does not claim to be trans, just a femboy.
Well sure but... Why? That's a great way to give a huge blow to your body for fun. Anyway, it's 4chan so whatever. In any case you are right, I assumed more than was stated.
People modify ("deal a huge blow to" in your words) their bodies all the time to fit certain preferences. Be it tattoos, piercings (including earrings), cosmetic surgery or even stuff like body building.
It is not that strange that people want to express themselves with their body.
Does it matter why? Bodily autonomy means bodily autonomy for everyone, regardless of whether you "understand" or or not. If he wants to be a more feminized masc, is it hurting you?
It might be in this case, but I would not object for a trans man to call themselves femboy if they look like a feminine boy, since for all that matters to me a trans man is a man.
You may not object but that's not how the word is commonly used. Anyone can call themselves anything, but for words to have any meaning we need to have a gentleman's agreement about when and how to use them, which is basically what a language is.
Anyway, I'm just explaining the word's conventional meaning. I have no interest in arguing with you as if I were some kind of linguistic prescriptivist.
I've heard from a few transfem lesbian friends that one of the hardest parts of coming out to themselves as trans was that it would also mean acknowledging they're not straight, because if you're someone who feels like you're failing at being a man, attraction to women can be pretty grounding. "It was the one normal thing about me" - whole lot of internalised misogyny/transphobia/homophobia.
But that's our assumption, it's true that it might just be a dude that likes being feminine, no trans involved.
Quite right; labels like straight get pretty wibbly in situations like this. I find it sad because the current prevalence of homophobia and transphobia makes it hard for us to collectively understand what would it mean to be a cis-het femboy who takes HRT — for us to conceptualise of a world where that isn't a contradiction. Bigotry makes it harder for people to explore their true selves, regardless of their gender or sexuality.