ありゃあ馬鹿馬鹿しいアイデアだったな。の英語

That was a stupid idea.

It was a bad idea.

that's a cockeyed idea

Sounds like a pretty good idea, after all.

What an absurd idea!

I hit on a good idea.

I hit a good idea.

I've got a splendid idea.

A wonderful idea just ran through my mind.

That idea was a masterstroke.

It thought and the good idea was on.

I had a good idea.

A good idea came to mind.

I just got a good idea.

Hrmm, I can't come up with a good idea.

I can't come up with a good idea.

What a senseless idea!

He thought how foolish he had been.

I thought of a good idea.

What a piece of folly!

Stop acting like such a fool.

Doing that was stupid.

Hey, that's a good idea.

Say, that's a good idea.

What a wonderful idea!

Listen, I've got a great idea.

A bright [happy] idea flashed across my mind.

A good idea came to me.

A happy idea came upon me.

A good idea! I never thought of it.