Thread: "Where do you get off....?"

seems reasonable that it is from some kind of figure of speech, maybe like '60's lingo, or earlier beat lingo.

"Where do you get off (the trip you're on)" : ego trip, power trip, bad attitude etc. This could easily start backwards from 'get off that trip you're on' and morph into the 'where do you get off (...)'
Just guessing.