A lot of the time people will say like "oh I'd never make fun of a disabled person" but then they do and they don't even realize that that's what they're doing. Like
People will say they wouldn't make fun of a schizophrenic or psychotic person but then make "jokes" about people being insane and delusional.
People will say they wouldn't make fun of epileptic people but then get mad about having to add flash warnings.
People will say they wouldn't make fun of an autistic person but then berate people for missing social cues.
People will say they wouldn't make fun of visually impaired people but then call people lazy for not reading things themself or making spelling mistakes.
People will say they wouldn't make fun of an intellectually disabled person but then mock people who can't do "basic" things.
I think it in part comes from the belief that the people you know couldn't possibly be disabled, that if you met a disabled person you'd be able to tell immediately. And, no. That's not how it works. If you want to be an ally to disabled people, you don't make fun of the things we do. Even if you're not making fun of someone who's disabled, you're telling the other disabled people you know that you're not safe for us to be around.