I found out through a friend who has ADHD just talking about it and finding myself saying "oh god I know EXACTLY what you mean" too often. Then I stumbled upon the reddit adhdmeme community and found myself laughind and saying oh god so true to many of the posts there. Funnily enough now that I'm diagnosed I am noticing that I have unconsciously surrounded myself and just meshed much easier with ADHD people. My wife also has ADHD for example and was always undiagnosed, the friends at work I mesh best with.. you guessed it, also ADHD. Then I learned about how its to a majority genetics and a couple of months after (independent, not somehow induced by me) by nephew gets diagnosed too.