2 sentences

1. 这完全是他的虚荣心在作祟。

   zhè wán​quán shì tā de xū​róng​xīn zài zuò​suì.

   This was purely his vanity at work.

   Source: Dong Chinese Dictionary

2. 他这样做纯粹是为了满足虚荣心。

   tā zhè​yàng zuò chún​cuì shì wèi le mǎn​zú xū​róng​xīn.

   He did this purely to satisfy his vanity.

   Source: Dong Chinese Dictionary