How do you deflect others when they try to tell you about your own disorder? Sometimes when I tell someone that I'm autistic they immediately respond with "well my cousin is autistic and you're nothing like him" or some other way of trying to subtly tell me that I'm not actually autistic and I don't really know how to stop that without sounding rude or escalating the situation into a serious argument. I have a professional dx from a psychologist, too.
Honestly there’s no reason for you not to be rude back to them at that point. They’re being rude by thinking they know better from interacting with you and often when these comparisons are made, they’re comparing a child they know very well to a teenager or adult they don’t know as well. (You didn’t mention your age so I’m sorry if that assumption is off for your specific situation.)
A counter I’ve seen a lot for this is ‘No shit, he’s a toddler and I’m not’. Of course if they’re comparing you to someone of your own age group this doesn’t hold up as well, but generally speaking pointing out that of course you’re not, you’re a different person will shut most people up.
For me, this is depending on the day either too confrontational or way too subtle though. There are times when it is very amusing for me to pretend to be as ‘uninformed’ as the people talking to me think I am and just watch them try and argue their case and most times during that come to the conclusion that I probably am autistic after all.
Other days I just flat out tell them they don’t know what they’re talking about and should mind their own business.
These are all valid responses. You do not owe them an explanation. You do not have to prove anything to anyone.
I hope this helps and if you need more help, feel free to send in a follow up.