2 sentences

1. 他嘿嘿一笑，显得有些得意。

   tā hēi​hēi yī xiào, xiǎn​de yǒu​xiē dé​yì.

   He gave a smirk, looking a bit smug.

   Source: Dong Chinese Dictionary

2. 他一个人盯着手机屏幕，在那儿嘿嘿傻笑。

   tā yī gè rén dīng zhe shǒu​jī píng​mù, zài nà​r hēi​hēi shǎ​xiào.

   He was staring at his phone screen, giggling foolishly to himself.

   Source: Dong Chinese Dictionary