Armor designed to masculine or feminine in appearance seems like a very human thing to do to me.

It’s important to note that “feminine” in this context does NOT mean “sexy”. Someone might consider it sexy, sure, but I’m not talking chainmail bikini nonsense here.

This wasn't specifically about The Mandalorian (I haven't watched), though people talking about it prompted the tweet.

What confuses me is it looks like the male Mandalorian armor has its own unnecessary pectoral definition. Are masculine cosmetics okay, but not feminine?

Sometimes, anyway. There appears to be variety in the armor. As I said, I haven't watched. For all I know, the lead's gone through several suits of armor.

I'm not trying to be snarky about that "masculine cosmetics" question, btw. It's a genuine question, and something I've noticed is that masculine characteristics seem to be treated as "default" and don't get commented on, and feminine characteristics are treated as anomalous.

This can have to do with anything from armor design to species design to robotics design, etc.

Androgynous also seems to pass without comment, but coded masculine seems to get an automatic pass while coded feminine will get some sort of reaction.