Though one thing I've known for a long time, perhaps not as embedded but still fun, is that Stephen Sondheim invented the phrase "everything's coming up roses." It was not a thing people said; it was a thing he devised.
I can't just this second think of another weird one-off phrase that has so embedded itself in the English language like "jump the shark" has.
I'd think that most people would have no idea whence it came had they not been specifically told.
