Ultimate Geek Fu

As we continue to wrangle about genres, sub-genres, micro-genres, and so on and so on, ad infinitum, a simple but powerful idea keeps coming to me. One of the problems with writing genre fiction in general, and fantastic fiction is particular, is the extraordinarily permeable nature of the boundary that separates the genre from the mainstream. If the tropes, conventions, conceits, idioms, vocabulary, etc. of the genre are successful enough, they invariably become mainstream.

So that's today's Ultimate Geek Fu question. What's your favorite example of a science fiction, fantasy, horror, or other SF/F genre idiom that was clearly SF/F, say, ten or twenty years ago, but is centered squarely in the middle of popular culture today?

Let the arguments begin.