I would have thought that the "trans women aren't women" crowd ought, in order to be consistent, also to be agreeing with the statement "there is no such thing as an effeminate boy or an effeminate man"
Shouldn't any way in which a male person behaves be, by definition, masculine?
That's what you get for thinking on behalf of other people.
But seriously...
I can only speak for myself, not for the entire crowd, but I would say that while I would disagree with your statement, I think it's close to something I would agree with.
I would say that no behavior is definitively male or definitively female. So, instead of saying that any way a male person behaves is masculine, I would say that there is no truly "masculine" behavior, regardless of how many men nor how few women engage in that behavior.
On the other hand, there are behaviors and mannerisms that are correlated with maleness. They are not definitive of maleness, but males typically engage in those behaviors and females typically do not. When I was in biology class, these were called "tertiary sex characteristics". I suspect that term is considered archaic today.
With regard to the "effeminate" label, then, I would say that as a means of classification, it is not very useful. There is no test that one can do to say that a person is effeminate or is not effeminate. Nevertheless, we can recognize the word, and the associated mannerisms. It means something to us, despite its occasional lack of clarity.
Similarly, although I said that there is no "truly masculine" behavior, the word "masculine" is still useful for describing the typical case. If I say, "He is very masculine." people still have an idea what I mean. There are behaviors and attributes very strongly correlated with sex, and we have descriptors for those behaviors.
However, no one in my "crowd" would say, "Hmmm....your behaviors are stereotypically female. You should use the women's locker room."
