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.
To be sure it's a play on the name of Gypsy's main character (though of all the Roses I've ever seen, only Imelda Staunton acknowledged it, for a half second, the first time she sang it), but it did inspire director Jerome Robbins to inquire "Everything's coming up Rose's what?"
