At somebody’s expense Definition 1 of 3Pro Tip 1/3Negative Impact Used when someone's actions negatively affect someone else, often for personal gain. He got the promotion at his colleague's expense. Pro Tip 2/3Emotional Cost Might imply emotional consequences like guilt or strained relationships. She achieved her goals, but at her friend's expense. Pro Tip 3/3Cultural Sensitivity Be aware this phrase can be sensitive; avoid suggesting selfish behavior. He won the argument, but it was at his partner's expense.