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
Whatever he does, it's none of my business.
That's not my problem. Figure it out yourself.
Variant using 事 for こと.
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'.