Most people do it ironically. I think the tradition started with 4chan and whatnot, since people on the spectrum usually have issues with social interaction, so the 4chan members, who are not very socially gifted, joked to eachother that they were autistic. From there it kinda spread.

hoi

Don't worry , i am Autistic too and people make fun of me and HOI

Hoi

Oi!