理直气壮的英文：
[Literal Meaning]
reason/fair/air/powerful
to be very self-confident for being right or justified

[解释]
理由正确充分，说话气势就盛。

[Explanation]
to be assured and bold with reason or justice

[例子]
她理直气壮地说她没有看到钱包，更不可能是她拿的。

[Example]
She was assured and bold with reason and said she had not seen the wallet and it would even impossible for her to steal it.

With justice on one’s side,one is bold and assured．
理直气壮

bold and self-confident;With right on one's side
理直气壮

Our representative justly and forcefully refuted the other side's fallacy.
我方代表理直气壮地驳斥了对方的谬论。

Therefore, we must confidently keep to the socialist road and uphold the Four Cardinal Principles.
所以，我们要理直气壮地坚持社会主义道路，坚持四项基本原则。

“Well,” said Miss Ophelia, energetically.
“不过”奥菲丽亚小姐理直气壮地说。

You must be certain of your facts before you start flinging accusations(around)(at people).
必须对实情胸有成竹才能理直气壮地(到处)指责(别人).