1. tell a blatant untruth
stop lying through your teeth, I know you were there
This idiom means to tell somebody something that you know to be completely false or untrue. To 'lie through your teeth' is to lie deliberately, without shame. The force of this expression means that to accuse someone of doing so can lead to conflict. That's why you would generally only say it to, or about, a person you are absolutely certain is lying. As the video shows, this expression is common in both a social and professional context and is similar to the phrases 'tell a pack of lies,' 'lie to one's face' and 'a barefaced lie'.