expression, godan verb (-su)
descend; stoop; degrade oneself; be reduced to
Idiomatic expression meaning to lower oneself socially or morally, often by engaging in unworthy behavior or falling into a lower state. Conveys a sense of personal decline.
彼は借金のために身を落としてしまった。
He degraded himself because of debt.
そんなこと
Don't stoop so low as to do such a thing.