I would venture to guess that Star Trek is the fandom with the most memes based on images and phrases solely from the source material. By nature of originally starting as a TV show, Star Trek has so much more source material in terms of runtime than Star Wars or Harry Potter. The funny thing about Harry Potter fans and their memes is when they’ve exhausted memes based on the books and movies, they just start making stuff up that has nothing to do with anything that actually happens in the series and treat it as if it’s canon. There are entire fanfiction universes that are inspired by no less than three pages in the original books about Harry’s parents, and people will take characters from said universes and act as if they’re as (or more) important to the canon as Ron or Hermione. When no good new material is coming out of your fandom, you really have to improvise.