You're full of it
Abbreviated Y.F.O.I.; An expression that means someone is lying through their teeth about something
Sarah: Did you know that I can do a full split without having my hands on the ground?
Jenifer: You're full of it. I saw you trying to do one a few days, but your feet were not that far a part enough to be a full split and your hands were on the ground.
Jenifer: You're full of it. I saw you trying to do one a few days, but your feet were not that far a part enough to be a full split and your hands were on the ground.