expression
that's not my concern; that's none of my business; that's not on me
A blunt, informal phrase used to disclaim responsibility or interest. Often carries a dismissive or defiant tone. Compare with the slightly more formal 知ったことではない.
See also: 知ったことではない
彼が何をしようと、私には知ったことじゃない。
Whatever he does, it's none of my business.
そんなの知ったことじゃないよ。自分で考えて。
That's not my problem. Figure it out yourself.
More formal and less dismissive than 知ったことじゃない. The じゃない contraction makes the phrase sound more casual and blunt.
A contraction of 知ったことではない (shitta koto de wa nai), literally 'it is not a thing I know'. The phrase is a set expression meaning 'it's none of my business'.