be mild and nice 和颜悦色

“和颜悦色”，汉语成语，意思是和蔼喜悦的神色，形容态度温和亲切。可以翻译为“with a kind and pleasant countenance，wearing a pleasant and gracious face，be mild and nice”等。

他和颜悦色地说：“我并不是想扫你的兴。”

"I didn't mean to upset you," he said mildly.

我会和颜悦色地对她。

I'd go easy on her.