Two-faced / Duas caras

From: http://www.bbc.co.uk/worldservice/learningenglish/language/2014/04/140410_todays_phrase_two-faced.shtml

White mime masks

Masks used in 'mime', a kind of performance art

Today's Phrase

If someone is two-faced, it means they say nice things about someone to their face, but say bad things about them behind their back.
Examples:
Matt is so two-faced. He told me I'm a great cook; then afterwards he told his other mates that my food is the worst he's ever eaten!
I really don't believe what Matilda says; I think she's a two-faced liar.

Take note

If someone loses face, they lose the respect of others.
Example:
Phillip lost face when no one came to his birthday party.

Interesting fact

The masks in the image are used in mime, a kind of theatrical performance which uses no words. Instead, actors use facial expressions and movements of their hands and bodies to tell the story.