kick (one) when (one) is down 落井下石

“落井下石”，汉语成语，字面意思是“drop down a stone on the man who has fallen into a well”，比喻乘人有危难时加以陷害（ to maltreat an injured person; add insult to injury; add to the misfortunes of a man who is already unfortunate），与英文俗语“ kick (one) when (one) is down”意思相近，表示“to criticize, exploit, insult, or otherwise treat badly someone who has already suffered a setback or is in a vulnerable position.”

例句：

最后我就是无法做到在吉米倒霉时落井下石。

In the end I just couldn't kick Jimmy when he was down.

杰夫的女朋友刚抛弃了他，我不想再落井下石。

Jeff's girlfriend just left him, and I don't want to kick him while he's down.