where do you get off

used in challenging a person who has said or done something offensive as an equivalent of the expression, “how dare you?”
where do you get off saying such a thing?
1. (inquiry) used when someone has crossed the line, in your opinion.

2. one of the very funny lines from the very unsuccessful film hot rod
1. friend 1: dude i just tony danza’d your ex girlfriend!
friend 2: where do you get off?

2. rod: where do you get off?
a question asked when someone has done something considered to be awkward, strange, and/or just plain odd.

a rather literal -n-logy: when on a city bus/train/subway/etc., you might meet some odd person. you might ask “where do you get off?” as in asking what stop they get off at, wondering if they live in a neighbourhood with strange folk.

probably not the true origin of the term, but that seems like a pretty good guess if you ask me.
guy 1: “so yeah, i like to run around naked with a ball of wool in my hand, and my cat chases me trying to get the ball of wool. it’s sooooo much fun!”

guy 2: “where do you get off?”
basically means “why are you…”, as in “why are you having s-xual relations with my wife, friend?”
or, as most of us would put it:

“where the f-ck do you get off f-cking my wife, -sshole!?”