That's not a pronoun though, that's a name. No one can know what social role this person is aiming for or how they want to be treated, as rabbits do not exist as free people in human society.

"I identify as a rabbit, treat me like a rabbit."

"What, do you want me to lock you in a cage and raise you as a pet or source of meat and fur?"

If a child wants to play make believe, and the adults around them want to humor them, that's fine. But we're talking about adults in the real world here.

Again, the only way anyone knows how to treat this person is by learning their very specific "pronoun." And if a word cannot form as a useful shorthand, it by definition isn't a pronoun. This person doesn't have "bun" as their pronoun. That's just their nickname.

And what's really odd in these conversations is that this has fuck all to do with trans people. Going by a quirky nickname you just made up doesn't make you trans or anything other than a person with a quirky nickname.

If you have to explain it, it's not a pronoun. If it has nothing to do with gender, it's certainly not a pronoun. And gender isn't just vibes. It has to have some actual relation to human sexuality and gender roles. Do you think your gender is a cat? I'm sorry, but you're real gender is apparently clown. The purpose of pronouns is traditionally to indicate male and female. And pronouns should stick to that axis, though nonbinary folks fit neatly into that.

To me, a pronoun is something that:

1. Is a useful and practical shorthand. (A pronoun is not a nickname.)
2. Maps to a real gender that has some relationship to male, female, man, woman. (Could be various forms of nonbinary that say you identify between male and female, as neither male nor female, etc. But it has to actually have some connection to male/female.)

I just fundamentally reject the idea that the definitions of "gender" and "pronouns" are so meaningless that you're basically using the word "gender" interchangeably with the word "vibe." We have so many words to describe "bunself" without muddying the word pronoun. You could just say some has a rabbit-like personality or character. There's no need for cis people to appropriate trans terminology for things that have nothing to do with trans issues or the gender spectrum.