That's a foolish action.

那是个愚蠢的行为。

Lying is one type of foolish action.

说谎也是一种的愚蠢的行为。

He deeply repented of his foolish action.

他对自己愚蠢的行为深感后悔。

With this foolish action he had damned himself.

他因这一愚蠢的行为毁掉了自己。

With this latest foolish action he has damned himself in everyone's opinion.

他最近这种愚蠢的行为毁坏了自己的名声。