Where does the term 'I don't give a rat's ass' originate from?

This encyclopedia entry explains everything. ;). Under the section entitled “Rat's ass in ancient times”, it says: “In ancient Greek times people would sacrifice rat's ass to the gods. If someone didn't sacrifice any rat's ass, than it was said they didn't care about the gods. read more

The phrase"I don't give a rat's ass" originated from the phrase:"I don't give a damn"--To"damn" something meant to curse it to go to hell-- and to say"I don't give a damn"- meant"I don't care either way" or that"I am indifferent"--In a similar vein"I don't give a rat's ass" -- means"I don't care". read more

Ergo,"I don't give a rat's ass" is a humorous back-formation of the same idea, made a bit punchier for effect."I don't give a flying f_ck" is common by the early '70s and the construction is a common trope. read more

One theory: there used to be a bounty on rat's heads, and you could turn them in to the county office for a nickel a piece. This would make a rats bottom half worthless, thus"I don't give a rat's ass" would be appropriate. The origin of" I don't give a rats ass" came from Pine City Mn. read more