Does fandom come with a Venn diagram?

I am perhaps a leeetle bit tipsy from a glass of wine (and tired, too), and keeping a happy ear out for my husband's chatting on the phone in what sounds like tips and validation for his upcoming interview. If you guys could spare some good thoughts for him around 3 PM CST tomorrow, that would be greatly appreciated.

So I've been thinking: what constitutes being in a fandom? Consuming the source material? Devouring the associated transformative works? Interacting with other fans? Trying to recruit people into your obsession? Or is it merely a self-determination, "I'm in the fandom because I say I am", or the converse of "I'm not in the fandom even though [X]"?

Because I could see an argument for any of those, or some overlap between them. I think I was in the Teen Wolf fandom before I started watching the episodes, just from reading the Sterek fic. I'd call myself a part of the NCIS fandom in that I've seen every episode and am bummed out by the news that Cote de Pablo is leaving, except that I can't stand the predominant ships (Gibbs/DiNozzo and Ziva/Tony) and only read the tiniest sliver of fic. I watched and loved Farscape and Buffy long before I met anyone else who did, way back in the days before I even knew what fandom was, but I don't think anyone could have said that I wasn't a huge fan.

What do you guys think?