I was just kidding 
I do not think any one of us can really learn that art. The simple reason is that what people hide in their chests (sadoor) and what they reveal is ONLY known to Allah. Avoiding people after getting certain gestures is probably the safest thing one can do and leave rest to Allah.
We do find out about the second or even third faces of people without having any art, believe you me. And that is because, at the end of the day, circumstances Allah creates, Unmask (and even mask) people around us.
Important thing is to have your heart clean of such things and have fear of what is the ultimate truth. People become two-faced because when they act so, their focus is this world whereas if the focus is shifted to where it is supposed to be, that is Day of Judgement, no one really would want to be two-faced… not that people are not aware of that… it’s just the amount of Iman in one’s heart…