짓이죠

is an act

→ 짓
phrase Uncommon #15,265
is an act 짓 means an act or deed and often describes behavior negatively. 이죠 adds a polite, confirming tone, like “right?”
KO: 그건 정말 무례한 짓이죠.
EN: That’s really rude behavior.

누구 짓 이죠?

Whose doing is it?

— 세 가지 색: 블루 (1993)

멍청한 짓 이죠,

It's a stupid thing to do, isn't it?

— 맥시멈 리스크 (1996)

무슨 짓 이죠?

What are you doing?

— 아모레스 페로스 (2000)

그렇죠, 완전 미친 짓 이죠

Right? It's absolutely crazy.

— 어바웃 타임 (2013)

이게 무슨 짓 이죠?

What on earth is this?

— 얼지마, 죽지마, 부활할거야 (1990)

바보 같은 짓 이죠

That’s a foolish thing to do.

— 이탈자 (1990)

천벌 받을 짓 이죠

It's something you'll be punished by heaven for.

— 홍등 (1991)