What a lot of people don't know about ADHD is that with it comes a likelihood of a delay in emotional maturity that leads to behavior that's not age appropriate. When looking back at my life, I can identify several times where I was behaving in a way that might have been expected of a child a few years younger than I was but wasn't appropriate for my actual age at the time. This effectively meant losing out on social opportunities, friendships, and romantic relationships. Most of my problems in life stem from this issue.
A mild example of said behavior is a time where I threw a fit in front of my girlfriend because my parents asked me to take out the garbage for them. I was living with my parents at the time and really didn't have many chores, so asking me to take out the garbage wasn't a big ask. But at the time I felt like they shouldn't have been wasting my time with that while I had my girlfriend over. Kids sometimes act out, yes, but I was 18 years old. That's even idiotic behavior for a 16 or 17 year old.
More extreme examples are the times I made inappropriate jokes or spoke my mind out loud without considering why other people wouldn't appreciate hearing them. I was also very judgmental when I was younger and for some reason thought the world ought to hear how judgmental I was, and I ended up losing some friends and romantic interests over that attitude.
It's possible there was nothing I could have done about it, so I struggle to actually regret it. What might have helped me was having an older brother or adult who could identify my behavior pattern, rather than dismiss it, and get me knock it off.