If you're my good friend and you do or say something upsetting, that's probably worth my getting upset. If you're not my good friend, but you do something to directly interfere in my life, like try to screw up my job or my relations with my good friends or family, then that's probably worth my getting upset. BUT if you're not my good friend (or not anymore) and you're messing up your own life, or other people's lives who I have nothing to do with, or doing something else that doesn't affect me, then it's not worth my getting upset. Sometimes I need to remind myself of that, and I'll probably put some distance between me and whoever is acting stupid so I don't have to talk myself out of being upset looking at their stupidity.
It's funny that when I point this out to other people, for instance people who are getting all riled up about their exes' behaviors towards other parties when said ex and other parties are no longer involved in their own lives, people tend to get all mad. If they'd look at WHY they are getting mad, or maybe just say, "Well, this is an area I still have conflicted feelings about and have to work on, so I need to think about it for a while even though it's upsetting me," I'd probably understand. However, my point is not to dis people's feelings, but rather that you spare yourself a lot of needless upset by just not giving a damn, 'cause not everybody is lucky enough to have a Dale-type flat-emotioned person around to remind them of that fact. Anybody who can't get my basic point without fussing at me probably deserves to sit around being stupidly overinvolved and miserable.