I tried in vain to start a conversation.
We looked in vain for the guide through three London parks. (Certificate in Advanced English; C1; German)
I made a vain attempt to engage him in conversation.
Many flew to cities in the vain hope of earning money, thus increasing the number of the homeless . (Certificate of Proficiency in English; C2; French)
He's terribly vain.
Men are vain creatures who worry, maybe exces[s]ively, about beauty and keeping up with standards of beauty set by society. (Certificate of Proficiency in English; C2; Spanish)