Okay, so, this is one of those times where it feels silly to use fandom discourse as a case study, but I think the UT/DR fandom and its backlash against Ralsei being transfem is a great example of how "femboy" is almost exclusively a transmisogynistic term.
So, the argument for the use of the term femboy, which many well-meaning people (including myself in the past) have made is that it simply refers to feminine men. That there must be *some* term for men who like presenting femininely to use and femboy might as well be it. Of course, you can ask why these people can't be referred to "feminine men", why there exists a need for a literal third gendered term in the form of a compound noun, if not to allow the men who are attracted to so-called "femboys" to rhetorically other them from maleness for the purpose of sexual objectification. But that argument gets into the weeds of arguing the linguistic significance of portmanteaus of adjectives and nouns, which is unlikely to go down well on a website where a significant number of people still say "transwomen".
It's much better to actually demonstrate *how* these words are used in practice. It is well established that femboy as a term was brought into the public conciousness as a "politically correct" alternative to the term "trap", which was explicitly transmisogynistic and nowawadays widely recognized as a slur. This was not the result of a conspiracy to create a dogwhistle or something, but rather the organic result of tension between certain leaders in western anime fandoms and their desire to not be seen as regressive in a world increasingly more trans-supportive, and those anime fans who wanted to continue their exact behaviour and attitudes towards transfem-coded and textually transfem characters in their favorite media, producing the term "femboy" as one of the most impressive linguistic sleight-of-hands in history.
While knowing that history is enough for some people to discard the term entirely, I don't find it a fully satisfying reason. After all, terms are defined by usage. So this is where I get to the actual case study.
In the latest chapter of the serialized release of the RPG DELTARUNE, a previously moderately transfem-coded character named Ralsei was confirmed more explicitly as textually transfeminine as part of their arc of finding their own identity separate from the wants of others, notably being conspicuously referred to with they/them pronouns in some of the games voice-of-god narration.
What's more important for this post than how Ralsei is portrayed in game is how large parts of the fanbase reacted to this. What was already a common response to transgender Ralsei theorist became a deafening overture in certain parts of the fandom: "we don't like this. It's *femboy erasure*". Similar arguments went: "This is just sending the message that all femboys are secretly trans women, people only read into this because [they're] feminine!".
Now, if you're familiar with Toby Fox games, you might already spot a pretty glaring flaw in people claiming that Ralsei's transition erases "femboy representation". Notably, *there are plenty of feminine men in Toby Fox games*. Notably, DELTARUNE Chapter 5 includes Blue, a black-coded male ballet dancer who presents very feminine, and yet, the people whose first reactions to Ch5 were to talk about how sad it would be to lose precious femboy rep didn't seem particularly enthused about this at all. Going further back, one of the main bosses of Undertale, Mettaton, is an even more openly feminine man who is even textually transmasculine, but yet people in the UT/DR fandom act like *Ralsei* of all characters is the last bastion of uncomplicatedly male characters who like presenting femininely.
People will often cite this as a gotcha, like it reveals an underlying ridiculousness to the arguments against Ralsei being trans, but I rarely see people reading more into the actual implications of it. Which is that Blue and Mettaton are not "femboys", despite being feminine presenting men. This should be obvious if you have been exposed to the term "femboy" enough that you have a subconciously understanding of its definition, you can just look at those characters and implicitly know they aren't "femboys". Because femboy has never meant a feminine man, it's always meant the exact same thing as "trap", that is, a transfem-coded character. A character who is confident in being male can never be a "femboy", only a character who demonstrates a complete alienation from masculinity. In real life, "femboy" doesn't refer to drag queens or other men who express themselves through femininity, but rather primarily to pornstars who dress like newly-out trans women (a significant portion of whom actually *are* trans women who are forced to adopt the label to appeal to men who, surprise surprise, want to be able to degender and sexually objectify them easier).
I don't have a good ending to this, but here's the call to action: keep a mental note about who does and does not get regularly called a "femboy", and ask yourself if that category is actually made up of any and every feminine man. And when it isn't, you'll see why a lot of transfems view the word as a slur primarily targeting us.
