My understanding is that RSD has more of a basis in feeling rejected (duh) and is more self centered - as in, you’re worried about you saying the wrong thing, not being accepted, what have you. Where as social and general anxiety can encompass that and also have more external fears about what in the world can go wrong. 
Also, as someone else said, you can develop anxiety as a result of rsd or other adhd symptoms, so you don’t have to rule out methods of treating anxiety by any means.
Hope that helps, I am not a pro in any way, just personally experience both rsd and anxiety

I just found out that RSD is a thing, and its characteristics sound a lot like the anxiety I face and I’m wondering, how do I know which one I have? Does anyone here have RSD and can tell me about how it affects them? Sorry if this is a dumb question, I only recently got diagnosed as an adult so I’m very new to the ADHD world!

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ADHD

RSD vs Anxiety?