それは愚かな行為だ。の英語

It is an act of folly.

That is troublesome behavior.

That is a stupid mistake.

That is too silly.

I am foolish.

That's a stupid question.

That's a stupid question!

It is such a stupid love.

That is a foolish tool.

He is acting a studied part.

plain folly

That is a mistake.

That is a misunderstanding.

That's so stupid.

a stupid fellow

That action is just like you.

That is an action that you would do.

It's so stupid.

That is the height of foolishness.

it is all patently nonsense

This is a downright swindle.

That is truly an absurd idea.

I am innocent of the charge.

That is a waste.

That is an extreme prejudice.

That is a horrible bias.

That is a stupid [not a very sensible] way of doing it.

Your conduct betrays a lack of good faith.

That is a misunderstanding.

It is an immoral action.