While watching Looney Tunes the other day on Boomerang (the particular episode was the Bugs Bunny/Yosemite Sam short "Bugs Bunny Rides Again, 1948) I heard Bugs say this line (and I may be slightly paraphrasing):
So long! Goodbye! Have a nice trip! Make sure you wear your overshoes in Chicago! Don't forget to write!
It's a "western", so the setting is presumably the late 19th century. Similar situation to many other times when Bugs confuses someone with his rapid-fire delivery, like other episodes when he sends someone on a "cruise" saying "Bon voy-ah-gee! Farewell to thee!"
So... it sounds like an insult to Chicago? Lots of mud and/or crap in the streets I guess? Is there something else I'm missing here?