Did you ever have a classmate that pretended to be a vampire or some other supernatural creature? How much did they commit to it?

Ever heared of the French nuns that caught a case of mass hysteria and started meowing like cats? I'll quote a section about it on Wikipedia:

In The Epidemics of the Middle Ages, an 1844 collection of works written by J. F. C. Hecker (and translated by Benjamin Guy Babington), a translator's note by Babington, citing an unnamed medical textbook, recalls the story of a nun who lived in a French convent during an unspecified time (presumably in the Middle Ages) who inexplicably began to meow like a cat, shortly leading the other nuns in the convent to meow as well. Eventually, all of the nuns in the convent would meow together for a certain period, leaving the surrounding community astonished. This did not stop until the police threatened to whip the nuns.

All the right winger panicked about "children identifying as cats" need to read this thread and remember that kids have always imagined weird things.

Also I knew one who was like that about being a horse.

I knew a girl in college who also believed she was a cat (this was 20 years ago). She would also scratch and hiss at people. Additionally, she would randomly meow in class. They would just sit there "cleaning" themselves as well, licking their hands and arms. She wore a pair of cat ears and a tail. It was immensely weird.