be quick to switch sides 朝秦暮楚

“朝秦暮楚”，汉语成语，字面意思是“serve（the State of）Qin in the morning and（the State of）Chu in the evening”。本指战国时期，秦楚两个诸侯大国相互对立，经常作战。有的诸侯小国为了保证自身的利益与安全，时而倾向秦，时而倾向楚。现在比喻反复无常，可以翻译为“change one's loyalty frequently，be faithless”或“be quick to switch sides”。

例句：

他岂是朝秦暮楚之辈！

He is certainly not the type who frequently switches sides.