What I've been told:
"You can't be autistic because you express empathy." (hey, I have a lot of practice! It's almost automatic in most situations, and it's sincere, if scripted)
"You don't sound aloof enough." (this is online, where it's easier to present yourself as you wish)
"You have theory of mind."
"You, a 41-year old adult, are different from a 10-year old autistic child I once saw in a classroom."
Strangely, one guy who seemed to have mostly negative attitudes about autism (he communicated what he was trying to say badly, I think, as he hasn't done it again), just asked me one question: "Do you need to move your hands a lot?" and when I answered "Yes", he said "Okay, maybe you are." And has been cool about it ever since.