To say something directly to one, especially when it is something critical, derogatory, inflammatory, or otherwise negative.
A: "Tom's been telling people around the office that you've been slacking lately." B: "If that's the way he feels, why doesn't he come say that to my face?"
I know she spreads a lot of nasty stuff about me behind my back, but she's too cowardly to say any of it to my face.