When a mentally unstable person has not been properly hospitalized and given medication, and has come to believe they are not human, superior to others, or somehow linked to an animal/fictional being spiritually. Like most batshit crasy individuals, their shit filled minds are impossible to flush clean and will deny any aspects of being human.
If encountered in real life, quickly call the proper institution in your area, and the men in white coats will gladly give them the desperate shock treatment they need.
Otherkin: IM A DRAGON!
Rational person: No, you're human...
Otherkin: STFU hyooman, before I burn you with my fiery breath!
Rational person: Idiot.. walks away