中英成语俚语800对129：反复无常
反复无常 Play fast and loose.
eg：One should not blow hot and cold with what one has promised.
中英俚语俗语来源：汉书：“齐夸诈多变，反覆之国。 ”
同义词：变幻莫测 The wind keeps not always at one quarter. 反义源：矢至不渝 Stick to it.