Definition
To behave in a strange, silly, or eccentric manner, suggesting a lack of mental clarity or being slightly crazy.
腦袋有喜鸭（形容行為愚蠢或精神失常）
Ever since he started talking to the air by himself, I've thought he has bats in the belfry.
自從他開始自言自語後，我就覺得他精神有些失常。
Her illogical decision made me think she has bats in the belfry.
她做出的不合理的決定讓我覺得她精神有些失常。
It was clear that he had bats in the belfry when he tried to comb his hair with a fork.
當他試圖用叉子梳頭時，很明顯他精神有些失常。