Unlocked description: You helped Carlo construct the perfect lie.
Passenger: Carlo Cerruti
I'm not sure if it is mandatory but I refused to help him first and then I accepted. For the lies I chose "stolen phone", "long lost friend" and "wierd guy that followed him". The achievement should unlock at the end of the conversation.
Thanks to Calex dEUS for confirming that it is necessary to refuse to help him first.