態度に

with regard to one's attitude

→ 態度
phrase Uncommon #8,847
with regard to one's attitude The particle に marks what something is directed at or concerns, so the best English translation depends on the sentence.
JA: 彼の態度に驚いた。
EN: I was surprised by his attitude.

態度に気を付けなさい。

Watch your attitude.

もうこれ以上彼のあのような不愉快な態度に我慢できない。

I can’t put up with his unpleasant attitude anymore.

彼女は彼の突然の反抗的態度にとてもびっくりした。

She was very surprised by his sudden defiant attitude.

態度に気を付けて。

Watch your attitude.

彼女は彼の態度に騙された。

She was fooled by his demeanor.

彼の顔つきや態度には軽蔑の気持ちが表れていた。

His expression and attitude showed contempt.

私は彼女の粗野な態度に腹が立った。

I was annoyed by her rude attitude.

彼の親切な態度にすっかり騙された。

I was completely taken in by his kind demeanor.

私はもう彼のあの意地悪な態度に我慢できない。

I can't stand his mean attitude anymore.

彼はその食べ物が気に入らないことをはっきり態度に示した。

He made it clear through his attitude that he didn't like the food.

態度に気をつけないとどうなるかな

I wonder what will happen if I don’t watch my attitude.

— コーラス (2004)

私は彼の態度に我慢できない。

I can't stand his attitude.

私は彼のあのいやな態度にはもはや我慢できない。

I can't stand his nasty attitude anymore.