同恶相济

tóng'è-xiāngjì

[sharing the evil and assisting the cause; the wicked support the wicked] 同是恶人而彼此互相济助, 为非作歹

暨诸葛诞滔天作逆, 称兵扬楚, 钦咨捕罪, 同恶相济。 --《晋书》