Let me start my review by a quote:
Lie through your teeth – Today, it means to lie through a smile – easily and unashamed. But its origins go back to the 14th century, when the phrase was to “lie in your teeth” referring both to the liar’s teeth, and the teeth of the person being lied to. The meaning was similar to today’s phrase of “lying in your face.”
In the case of WhyRU episode 6, its lying through your kiss as Zee’s Tutor kept on repeating himself that all the concern and shower of affection for Saint’s Tutor are nothing but “tease”.