My favorite example is "nimrod."
Nimrod in the Old Testament was a great hunter archetype. Fast forward to the 1960s, and Bugs Bunny uses it to insult Elmer Fudd--basically calling him a great hunter sarcastically. Too few people understood the reference, but gleaned the idea Bugs was going for, i.e. to make fun of Elmer. From this, nimrod came to mean "dummy."