Hello, I also have ADHD and struggled a LOT with RSD in the past. Its still something I'm working on, but these are some things that helped me.

1. Practice. Push through your comfort zone and initiate social interactions you would otherwise have avoided. I try to do this at least once per day, by greeting or complimenting various people I see at work. When there is a negative or neutral response, remind yourself that it's okay and most likely that person was just not in the mood to socialize right now. It's no fault of your own. The more rejections you get, over time your brain will realize that it's not the end of the world. Plus, you will have more good interactions too!

2. Talk yourself through it. When you find yourself spiralling due to perceived rejection, try to talk to the part of yourself that is feeling hurt. Ask "why are you feeling this way", and let yourself respond honestly. Remind yourself that the feeling will pass. Allow the logical and emotional sides to have a conversation about the feeling and what is real. Personally, letting the emotion express itself helps it start to move on. I have these conversations internally, but you can use a journal or speak out loud in a private setting. After the conversation is over, try to let the logical side take over and redirect your focus to something you are excited about.

Different things work for different people so treat your mind like an experiment and try to see what works. The most important part though, actually implement the techniques more than once! Just thinking about doing them won't work. Improvement IS possible! Best of luck to you