Saying something (usually mean) about someone, and when confronted straight up denying - and even saying the opposite of what you had said.
Shelby: OhhEMMMGEEE Helga is such a whore!
***5 minutes later***
Anne: Shelby is Talking Shit about you
***10 minutes later***
Helga: So I'm a whore?
Shelby: What? Who said that? That is so mean! I can't believe anyone would call you that!