역대급 /yeok-dae-geup/
Best/worst of all time
Used hyperbolically to describe something at a historic level — can be the best or worst ever. A go-to intensifier for dramatic statements.
Examples
이번 시험 난이도 역대급이었어
That exam was the hardest of all time
역대급 콘서트였어
That was the best concert ever