An exact match:
I don't know shit about shit!
From The Slangman Guide to Dirty English: Dangerous Expressions Americans Use., by David Burke:
"I don't know shit about shit, but I know right from wrong!"
From An Uprising of Angels, by Marc D. Baldwin:
“I don't know shit about shit. Okay?
From Four-letter Films: Taboo Language in Movies, by Gabriele Azzaro:
Look, I admit I don't know shit about shit.
In all of the above references, the meaning of the phrase is roughly: I know very little about [things] that are worthless to me, which is derived by combining the meaning of the slang phrase don't know shit and the slang shit.
The slang shit refers to, among other things, a worthless person or thing:
From Oxford Dictionaries Online
noun ...
2.0 A contemptible or worthless person.
3.0 Something worthless; garbage; nonsense:
The common slang expression: not know shit, builds off of the meaning of shit, and means that the subject knows nothing:
From Oxford Dictionaries Online
Not know anything.
If someone says: I don't know shit about politicians, they are implying that they know [or care] extremely little about politicians. When someone says: I don't know shit about shit, they double down on the contempt, by implying that the matter at hand is worthless, and they know [or care] very little about it.
Not wishing to double down on a taboo, one might choose a slightly more formal,
I don't give a shit:
(about someone/something)
tv. to care about someone or something. (Usually objectionable. Often
negative.)
I don't give a shit about politicians! This approaches the exact match, because people who don't give a shit about shit, don't know shit about shit.
Many diminish the taboo (and contempt) by replacing the word shit with:
Adding the word flying into the expression seems to increase the sense of antipathy.
I don't give a flying:
- f#@&
- fig
- shit
- fart
- leap
- flip
- hoot