The hard truth about autism acceptance that a lot of people don't want to hear is that autism acceptance also inherently requires acceptance of people who are just weird.
And yes, I mean Those TM people. Middle schoolers who growl and bark and naruto run in the halls. Thirtysomethings who live with their parents. Furries. Fourteen-year-olds who identify as stargender and use neopronouns. Picky eaters. Adults in fandoms. People who talk weird. People who dress weird.
Because autistic people shouldn't have to disclose a medical diagnosis to you to avoid being mocked and ostracized for stuff that, at absolute worst, is annoying. Ruthlessly deriding people for this stuff then tacking on a "oh, but it's okay if they're autistic" does absolutely nothing to help autistic people! Especially when undiagnosed autistic people exist.
Like it or not, if you want to be an ally to autistic people, you're going to have to take the L and leave eccentric, weird people alone. Even if you don't know them to be autistic. You shouldn't be looking for Acceptable Reasons to be mean to people in the first place. Being respectful should be the default.