in the middle of nowhere/to the back of beyond (but imbued with sarcasm)

Hi! Does anyone know a synonymous idiomatic expression for “in the middle of nowhere”, but one that denotes rude sarcasm. Here’s an illustrative context in which such a sarcastic expression might occur:
Jack is annoyingly curious, and sees John going somewhere, and, as is his custom, asks John intrusively, out of excessive curiosity: “Where are you going?” to which John, annoyed, replies sarcastically: “‘To the back of beyond!’ and thinking in his mind: and far away from you”. Can anyone think of a idiomatic reply which would be rudely sarcastic, because the idioms I have used are a bit soft, and do not convey the great intensity of John’s annoyance.