In a bit of a rant here.

[dfangd]

Well, they're most likely attention seeking children who are using their (most likely newly found, and not genuine or authentic) title of "otherkin" to seem special or impressive. Honestly, when they realize that parading the idea of a mythical creature (or even a very real one) trapped inside a human's body is more of a form of social suicide than anything else, they'll probably drop their facade like a hot potato. The best advice I can give is to let it be. Allow these immature children to believe and say what they will. It doesn't matter if they say you cannot be otherkin. If someone said that you weren't human, would that make it true? Honestly, talking to them will make no difference. I would not draw attention to the fact that you are otherkin either... people will not take kindly to it, just as these kids will find out in due course.

Just keep your head low and roll your eyes when they get pompous. It's not worth getting involved.
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.:. Nasroniala .:.

[albvan]

I'm just fascinated by the fact that some people completely lack the ability of critical thinking. It's like it occured to them out of the blue that they should be otherkin. And it's not just that. How can they be the only ones? They have an ego the size of a mountain. I'm always for discussion and correcting wrongs, but in this case it would be like throwing margaritas ante porcos. It's just a waste of your time.

[Namhias]

I have nothing more to add to this topic. I think they're attention junkies who just found another thing to "brag" about. It's particularly stupid to commit social suicide like this. Most likely, they do it for the attention, any attention is good in their eyes, positive or negative.
I'd just let them be, if they are the way you describe them, than they're pretty shallow and not worth your time. Talking to them about it will most likely end up you getting ridiculed by them, so I think that it wouldn't really matter.
I'd let them blow off some steam, if no one pays them any attention, they'll most likely abandon the idea of being an otherkin.

[Raven]

*Points to above posts*

Everyone's basically said everything. I'd (well, I wouldn't, but the part of my brain that's smarter than me would) ignore them. They say they're the only ones who can be otherkin? So? That's not something they can impose on you. If you're not the type to run around screaming you're an otherkin than such a threat has no effect.
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The Lichen grows slowly, atop of a rock.
It doesn't think, it scarcely feels,
But mightn't it be somehow greater than we?

[Hyraxylos]

[Namhias]

[Roark]

Okay last Friday I had an interesting chat with them, and just as you said they ridiculed me. First thing they said was You can't sit here case you're not one of us I told them to shut the mm up, and pleaded my case.
At one point one of my eyes glowed[As in went to a slit] which surprisingly freaked them out.
Hmm turns out you were right these idiots were all talk and no walk. Anyway after the talk they started trying to befriend me. And they STILL believed they were otherkin. Regardless I told them if they want to masquerade as otherkin by all means, just don't say you're that and no one else is so in this case there was no bloodshed just dialog and then some.

[dfangd]