Atypical depression doesn't seem at all to be atypical. mood reactivity to positives and interpersonal rejection sensitivity aren't unusual, right?

Atypical Depression: It depends on easily one is reactive and to what degree.

A matter of degree: To some extent, these feelings have been experienced by everyone. It is the degree to which they affect your day to day living which makes the difference. Extreme and/or lasting responses which impact one's ability to function or feel OK are less typical and can be addressed quite well in psychotherapy.