Is there something that you tend to "geek out" or "nerd out" about?
Harry Potter, Sherlock, pandas
Space related anything.
Tfios, divergent, the hunger games
H.P. Lovecraft and horror movies.
Shakespeare. If you even mentions something Shakespeare related, I have a geek out moment. Last week I toured a campus that had a lecture hall called "Montague Hall" and I could not contain myself. The tour guide had no idea what I was talking about.
It's also true for anything related to Doctor Who, Sherlock, Harry Potter, knitting, my hometown, other slight obsessions of mine.