It was a pretty stupid thing to do.

做那样的事实在愚蠢。

《牛津词典》

It was a stupid thing to do, I admit.

我承认，那次干的是件蠢事。

《牛津词典》

This was a very stupid thing to do.

这是无比愚蠢的。

youdao

It was a stupid thing to do and we apologise for any offence caused.

BBC: Obama effigy burnt by St Andrews Conservative students

In retrospect, it was a highly effective but incredibly stupid thing to do.

FORBES: 'Super Rich' Law Professor Retires From Blogging After 'Electronic Lynch Mob' Attacks His Position on Taxes

This story is further proof, as I have written previously, that stealing art is a really, really stupid thing to do.

FORBES: FBI: We Know Who Stole The Isabella Gardner Paintings