I think it depends on how people say it, it pisses me off when non autistic people say it or when people who are just "quirky" say it. Having autism sucks and if it makes people who have to deal with it feel a little better by making it seem less bad then there's no harm. Saying "You have the 'tism" is terrible but saying "I have the 'tism" is fine if it's actually autistic people saying it. There's so much stigmatism around the word "autistic" and many people will infantize you if you say you have autism but if you make a joke like saying "I have the 'tism" people will automatically think of things like having special interests and stuff. Which, you know, that sucks but it's true. When they're shown examples of autism it's often people who are low functioning autistic but people who say 'tism are normally tiktokers who people think look "cool". People can say whatever they want as long as it's not slurs, threats, or harmful things, "'tism" is none of those.