To appear outwardly impressive or brave, but in reality be timid and cowardly; a paper tiger.
他虽然平时总爱吹嘘自己如何勇敢，但在关键时刻却总是凤毛鸡胆，不敢承担责任。
Although he always boasts about his bravery, at critical moments he always proves to be outwardly impressive but actually timid, afraid to take responsibility.
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