勝手だ

It’s up to [someone] to decide.

phrase Uncommon #14,862
It’s up to [someone] to decide. Often used to assert that something is someone’s own choice or business; it can sound defiant.
JA: どこへ行こうが、おれの勝手だ。
EN: Where I go is up to me.

誰と寝ようと勝手だ

You can sleep with whoever you want.

— ブエノスアイレス (1997)

どこへ行こうがおれの勝手だ

I can go wherever I damn well please.

— さらば、わが愛/覇王別姫 (1993)

それはお前さんの勝手だが―一体正しい人間なんているのかい?

That’s up to you—but is there really such a thing as a truly righteous person?

— 羅生門 (1950)