Tight Lipped: In this one, the lips are tightly stretched across the face forming a straight line and concealing the teeth, this smile is not so much used by liars as by people who have secrets or are withholding their true opinion or attitude towards something.You can observe this one amongst women who say something like; “That dress is really gorgeous and looks beautiful on you” followed by a tight lipped smile instead of revealing their entire thoughts and ending; “….you fat cow!”.It’s also used as a polite smile by someone who doesn’t like her company but doesn’t know how to get rid of them. Font: http://sapientology.com/tag/types-of-smiles/