“His nibs”Remember this scene? It’s something a lot of Brits would have heard

“His nibs”

Remember this scene? 

It’s something a lot of Brits would have heard of before and might have used in their conversation, but it could have baffled non-natives. 

The Oxford English Dictionary, usually the definitive word on origins, defines “his nibs” as “a superior; a self-important person.” But as to the genesis of the phrase, the OED comments only “origin obscure.” 

If one digs around in other sources, some things come to light.  To start with “nib” was a seventeenth-century university slang term for a first year student at Cambridge University.

“His nibs” first appeared in print about 1820, but is presumably older. It was a common slang phrase in the late 18th and early 19th century to refer to an upper class male, someone of wealth and social standing. By the late 19th century, among English university students it was usually a sarcastic reference to someone seen as aloof or stuck-up. 

Along with an earlier form “nabs,” “nibs” was based on “nob,” an alternate spelling of “knob” and an 18th century slang term for “head. The “head” in question was both literally the human head and “head man,” or an important person. The word “nob” is British slang for a person of wealth or social importance.

In all cases, it is a derisory term, used to mock a person of authority, particularly one who is demanding to the point of tyranny - and takes the place of “His Majesty” or “His Highness” in a sentence.

Mary is being more than a little bit sarcastic and jealous here.