I'm sorry you learned this the hard way.
My parents were born in the 1930s and were raised in Catholic schools which literally "put the fear of God" in them. Basically for them, it was "be polite, follow orders, or your soul will go to Hell." Things were different when I grew up in the 1970s, but my parents remembered what things were like when they were kids. They taught me at a very early age to always say "Please" and "Thank You" when speaking to people. Years later, a co-worker taught me to use "Good morning" or "Good afternoon" in emails and phone calls to both clients and co-workers to make a good impression. At times, it felt like overkill, but I always did it, and never heard one person complain about my using those words.
Each written or verbal communication is an opportunity to impress someone and make them feel valued and listened to. Use friendly language like "please," "thank you," "good morning," or "good afternoon" whenever you communicate with a business person, PARTICULARLY if it's a potential employer -- unless you really don't want the job
I'd go so far to say that if you ever found a potential employer that didn't appreciate you using such words, they're probably not friendly themselves, so you wouldn't want to work there anyway.
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DSM-5 Diagnosis: Autism Spectrum Disorder, Without accompanying intellectual or language impairment, Level 1.