stoop so low

stoop so low (as to do sth) {fml} (to drop your moral standards far enough to do something bad, unpleasant or morally wrong, which you do not normally do) — (так) низко пасть; так опуститься; опуститься до того, чтобы сделать что-л.

Example: She was unwilling to believe anyone would stoop so low as to steal a ring from a dead woman's finger. (OALD)

stoop to sth / doing sth (to drop your moral standards to do something bad or unpleasant)

Example 1: You surely don't think I'd stoop to that! (OALD)

Example 2: I didn't think he'd stoop to cheating.

Example 3: I didn't expect you to stoop to lying.

stoop to somebody's/that level — опуститься на чей-л. уровень, стать на одну доску с кем-л. (осужд.); ≈ уподобляться

Example: Don't stoop to her level. — Не опускайся до ее уровня. Не уподобляйся ей.