MAHOGANY!

First book

What does that have to do with perfect couples not existing?

Well, in the second film Effie's character also mentions it again (I think along the lines of praising President Snow's interior decorating, saying his mahogany panelling is lovely), which the actress who plays her improvised, as she knew that the fans liked her previous 'mahogany mention'. In this way, it's become a bit of a thing within the fandom, about how she loves mahogany. :)

Huh. Esoteric fandom jokes kinda fall flat when they need this much explanation.

I don't think it's too esoteric. Just depends on your own readership, I guess - the HG is quite popular, so I'd have thought quite few people get this post.

The thing is, I'm remembering a mahogany gag from a vastly different movie with James Wood.

At least you're still getting a bit of humour out of the post through you remembering that, even if you didn't get the HG reference :)