expression
that's none of your business; mind your own business
A set phrase used to tell someone that their concern or help is unwelcome; similar to 余計なお世話.
See also: 余計なお世話
「どうして結婚しないの？」「いらざるお世話だよ。」
"Why don't you get married?" "That's none of your business."
彼の服装に口を出すなんて、いらざるお世話だ。
Commenting on his clothes is just meddling.
More common and slightly stronger; いらざるお世話 is a bit more formal or literary.
From 要らざる (negative form of 要る, 'to need') + お世話 ('care, help'). Literally 'unneeded care'.