“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.”
zuì hòu wǒ jiù shì wú fǎ zuò dào zài jí mǐ dǎo méi shí luò jǐng xià shí
In the end I just couldn't kick Jimmy when he was down.
jié fū de nǚ péng yǒu gāng pāo qì le tā，wǒ bù xiǎng zài luò jǐng xià shí
Jeff's girlfriend just left him, and I don't want to kick him while he's down.