3 sentences

1. 真是固执的姑娘，这么任性！

   zhēn shì gù​zhí de gū​niang, zhè​me rèn​xìng!

   What a stubborn girl, so headstrong!

   Source: OpenSubtitles

2. 由于父母的娇惯，他从小就很任性。

   yóu​yú fù​mǔ de jiāo​guàn, tā cóng xiǎo jiù hěn rèn​xìng.

   Because of his parents' spoiling, he has been willful since childhood.

   Source: Dong Chinese Dictionary

3. 这些任性的孩子在课堂上大声喧哗，老师很难管教。

   zhè​xiē rèn​xìng de hái​zi zài kè​táng shàng dà​shēng xuān​huá, lǎo​shī hěn nán guǎn​jiào.

   These wayward children make a lot of noise in class, and the teacher finds it hard to discipline them.

   Source: Dong Chinese Dictionary