にたにたwith a broad grin, smirking

ニタニタと笑(わら)う彼(かれ)は不気味(ぶきみ)だ。

His smirking is creepy. {with a broad grin, smirking}

人前(ひとまえ)でニタニタと笑(わら)うのは少(すこ)し失礼(しつれい)です。

Smirking or smiling broadly in public is a bit rude. {with a broad grin, smirking}

馬鹿(ばか)にしたようにニタニタと笑(わら)われて不愉快(ふゆかい)だった。

I felt unpleasant being smirked at as if I was being made fun of. {with a broad grin, smirking}

ニタニタと笑(わら)っていたら、同僚(どうりょう)から薄気味悪(うすきみわる)いと言(い)われました。

If I was smirking, my colleague told me it was creepy. {with a broad grin, smirking}

人(ひと)を不快(ふかい)にさせないように、人前(ひとまえ)ではニタニタ笑(わら)わないようにしている。

In order not to make people uncomfortable, I try not to smirk or smile broadly in public. {with a broad grin, smirking}