What did Knockerbicker/Knickerbocker mean in past times?

Answer 1

Knickerbocker was a slang term that meant any New Yorker of Dutch descent. It was named after the plumed breeches that the Dutchmen wore. They were called, "Knickers."

Answer 2

It still does mean your are from the Empire State of New York.

It originally meant that you were a Dutch Settler of New Amsterdam what New York was called but the Dutch