Definition
To act unfairly or dishonestly towards someone, typically without their knowledge.
背后诽谩人、背后做小动作
He felt betrayed when his colleague did the dirty on him, causing him to miss the promotion.
当他的同事背地里对他使坏，害他错失升职机会时，他感到被背叛了。
She will never forgive her friend for doing the dirty on her by dating her boyfriend.
她永远不会原谅她的朋友背地里和她男朋友约会。
In business, you have to be wary of competitors who might do the dirty on you and try to steal your deals.
在商业中，你必须提防竞争对手可能会背地里对你使坏，试图抢走你的交易。