male with breasts is currently being used in a bizarre way that breaks tagging for the posts it's used on.
The current rule, written in blood sweat and tears, is that if a character's canonical gender is different from how they are portrayed in a post, that specific portrayal, not the canon, should be used in that post's tags.
But male with breasts is being used as a loophole; taggers have been using it for any character they personally interpret as a male, instead of newhalf.
Despite the male with breasts wiki explicitly saying "Use this tag when the character has no penis or testicles visible, otherwise it should be tagged as newhalf." over a third of the posts in male with breasts are tagged with penis, bulge, or erection.
Despite most of the posts in male with breasts being counter to both the established conventions of Danbooru, and the male with breasts wiki itself, most of these posts are heavily litigated and subject to many tag wars.
There are really 3 distinct types of post in male with breasts: Characters who look completely female but are canonically male, nonhuman characters who look androgynous but are canonically male, and transgender/newhalf depictions of characters that taggers think of as otoko no ko. I'll use an example for each one.
Namine Ritsu is a character who is canonically an otoko no ko, 150cm tall, and has missiles on his torso that look like breasts. If we were to tag every post in namine ritsu according to canon instead of what's actually depicted, male with breasts wouldn't even be applicable, since they're canonically missiles and not breasts. Secondly, every post in namine ritsu should be tagged miniboy since the character is only 150cm tall in canon. There's no reason for something post #7270944 should be in male focus. He can be a male in canon, and 1girl or 1other for tagging.
Angel Dust is a barely humanoid devil monster from some cartoon that's "canonically male" so a bunch of stuff like post #7131842 gets thrown in there. Weird, nonhuman, genderbending characters is exactly what 1other should be used for.
And the worst offender: Bridget (Guilty Gear) was subject to like an 80 page thread the conclusion of which was "tag according to what's visible in the image" and yet things like (nsfw) post #6719843 or post #7574859 still get incessantly tagged male with breasts. And it's not being added by random burner accounts, most of the people I see warring over this tag are builder+
I understand that people want to tag things according to canon (or their idea of canon) and I think should whenever possible. But we just have to accept that for certain characters that are gender nonconforming in some way, what's in the image has to take precedence.
The only good use case for male with breasts I can think of is (nsfw) post #7108321, post #4950722, or (nsfw) post #7157434, which depict masculine characters with breasts. All of the other stuff is either newhalf, 1girl, or 1other
One last thing: I'd like to humbly beg that we stay on topic and and not turn this into the Bridget (Guilty Gear) gender thread again.