How do you make people think you aren’t incompetent?

Welcome to fluther!
I have physical disabilities.
My son is autistic.

I get it.

I feel that frustration. People judge. There is a valid evolutionary reason for that. Humans are carnivores. Some humans claim a vegetarian life, but their DNA is carnivore.

Animal behavior follows patterns. There are nocturnal, diurnal, herbivore, carnivore, hunters, scavengers, grazers.

If you watch, most herbivores run when confronted by carnivores. However, carnivores encountering other carnivores, they watch each other. They observe. Is this hunter a threat? Will this hunter drive away my future prey? If I just wait, will this hunter move on?

Mostly humans have overcome the study of each other, not completely, but mostly.
So, we can’t hope for humans to stop sizing up each other. We are designed that way.
All we can do, is be surprisingly more than they expect. It chips away at their hasty judgements. Little by little, some change their way of looking at people.

Consider yourself a diplomat, an official who represents people on the spectrum. That is what will earn you respect. Someday you will find yourself feeling pride, when you see proof you have changed someone’s attitude about you, or maybe others on the spectrum.
Then you will see yourself differently. That will show, and carnivores will judge you differently.

Going off the deep end will not make you seem competent.
It will only convince people you are unprincipled.

I listen carefully to people I’m interacting with and choose my words carefully.

Start with yourself and make sure you don’t feel you are incompetent. Everyone is good at something and you should concentrate on what interests you and what you are good at. Everything else then follows from that.

Don’t try to imitate those around you, follow your own star and choose your role models rather than having them thrust upon you.

Some thoughtful advice above… I like @Patty_Melt recommendation to be an ambassador of whatever ‘type’ people have you as.

And @flutherother advice to not feel incompetent – be solidly confident in the abilities you know you have. The corollary is agreeing with the ‘expert’ so they get the sense that you understand just fine – not lying of course, but where you already do agree with them make that abundantly clear without sounding like you’re kissing up.

You can’t make people think anything.

You can preset and carry yourself confidently, as the other people have said above. But ultimately they make the determination based on what they see. All you can do is be your best.

You aren’t putting the intelligence your writing clearly demonstrates to good use. You are in truth reacting like a 5 year old. Those “deep end” fantasies are easily fulfilled and you know it, but you are fortunately too smart to believe they will elevate your self esteem. We all want to be admired and perhaps envied, but nothing is quite so hollow or grows so annoying as the admiration from passing strangers over superficial veneers. Whatever you perceive as your disadvantages, they place you in an ideal position to study and weigh people’s reaction to them. And believe me, if you devote time to studying the people rather than their reactions to you, you will quickly conclude that most of them aren’t worth the effort to sway them one way or the other, freeing you to concentrate on the few who matter.

Focus on yourself. Don’t worry too much what others think and how they react to you.

I’ll answer specified to the question. I honestly think it is not what you need to read, and I am sorry, but I am literal. I am answering it anyway because you did a specific question, and I have information.
You need to read what neurotypical people that learned too many things in their lifetime have to say though.
They are people like Patty_Melt.
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Here it goes

My advice based only on observation, you should wear clothes that the majority of girls uses and starting find patterns in their phrases and body language (it always have), and copy it.
But if you find patterns in some sentences and try to use it in social situations observe the context beforehand, and avoid to use that sentence repeatedly.

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But people in the autism spectrum disorder usually have poor motor skills, and the usual reason for social success is body language (that requires motor skills).
Though It is well discussing these days that girls in mild autism are good actresses, so let’s hope you are one of those. And if you are not, I think you still can learn a bit.

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Social interactions are naturally complex and impossible to perform it with 100% success.

Years ago everyone thought I was vulnerable.
But until I become respected as in nowadays I had to learn people’s body language, fashion and to pick up patterns of sociolinguistic to avoid future abuses—the majority is cautious towards people of high class, so I thought that would be safe to copy the high-class behavior.
My advice is that you try to figure out what moves people’s minds. Psychology is hard for girls in the spectrum, but we still can find behavior patterns that are simple to understand.

Psychologist, neuroscientists, and teachers are the ideal to talk with and explain patterns in humans behavior because they are experienced in life and knows better.
And people like Patty_Melt.

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But if you want to try here it is:

1. Dress (considered by majority) better.
2. Learn patterns of talking and find the right thing to be told and at the right time.¹
3. Search for body languages.
4. Do question to someone about any situation that you feel misunderstood before accepting the anger.
5. Use a dictionary and a slang dictionary (but always read more than one meaning about slangs).

¹It is stressful if you don’t have someone to talk about what you are thinking of it, so you need someone else to listen about your negative feelings, for example, a psychologist.
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And ask people to stop telling others about your autism. At least say to them to be careful with who they’ll say it until that you have enough social understanding (and communication skills).
Tell them that it is for your progress to independence and that you deserves it.