You post a topic, list, category, whatever, in comments. (examples: "Five Dates X Regretted Going On," or "Five Fannish Gatherings that Y Attended"). I'll answer with a list of five things.
Any fandom I've written for or blithered about here is fair game :-).
ETA: these are going slowly because I think of two things for a list and then life happens and I lose my train of thought. But so far we have:
five times Duv Galeni was still David Galen
five times Lesley May didn't think about her face
five times Lady Alys changed Barrayar at a party
five times Cordelia was proud of Miles
five times Ges and Aral should have broken up, but didn't
five reasons Lady Alys envies Professora Vorthys
five holocubes Theisman kept
five things Theisman and LePic did for the Republic
five times Cordelia said 'Barrayarans!'
Crossposted at http://philomytha.dreamwidth.org/10