sir, this is an Arby's

Meanings

1. Used to indicate that one finds a statement to be bizarre, tangential, or inappropriate for the context in which it is made.

Etymology

From a humorous Internet meme that envisions a character giving a strange, rambling monologue, with the punchline being a fast-food employee reminding them that they are in a restaurant; Arby's is an American fast-food chain. This format of joke is first attested in a November 2011 tweet by American screenwriter Ethan Hunter (@ethanhunter).