to seduce / hook up with the girlfriend / female partner of a friend [colloquial]
Definitions (粵典–words.hk)
動詞、俚語
勾引朋友嘅妻子 to have an affair with the wife of one's friend; literally: to hook the righteous wife of one's older brother
江湖中人最忌三樣嘢,洗馬檻、着紅鞋、勾義嫂。
江湖中人最忌三样嘢,洗马槛、着红鞋、勾义嫂。
gong1 wu4 zung1 jan4 zeoi3 gei6 saam1 joeng6 je5, sai2 maa5 laam2, zoek3 hung4 haai4, ngau1 ji6 sou2. There are 3 crimes that triad members hate: to steal from a friend, to be an informer for police, to have an affair with a friend's woman.