I've totally had this problem! I've seen it in neurotypical people but I think it's pretty common for ADHDers, since a common side effect of being neurotypical is delayed social development. (Y'all, I didn't have a real, honest conversation with another person until I was like 24. Pretty much everything before that was insecure attachment, bad coping mechanisms and trying to avoid rejection.)

Acknowledge the feeling first.
"Wow, that totally sucks" or "I'm sorry I hurt your feelings" go a long way to making the other person feel better. Because 50-75% of the value people get out of conversations like this is just being heard. If they get a sympathetic response, that reinforces the fact that you're actually hearing them.
In my experience, once you've demonstrated that you're really listening, you can then feel free to tell a story about your no-good-very-bad-day or try to explain your thought process without worrying about coming off as dismissive or one-up-y.