I outed a liar once by misleading them. My coworker at a daycare claimed I had left early, leaving a bunch of kids alone. From previous interactions with her, I knew that she hated me because she wanted someone else to get my job. Also, she never came to check on those allegedly left alone children, which led me to believe she had made it up on purpose. So I said to her, "Lot's of people drive beige toyota camrys, are you sure it was me you saw?" She said yes, that she had seen me get into my beige toyota camry and leave early. I responded that it couldn't have been me, as I didn't have a car like that. I said that in front of the boss, who knew that the other woman was a liar in a way that me just protesting my innocence wouldn't have. Maybe it was rude, maybe it wasn't under the circumstances since she made such a serious accusation, but it was certainly effective.
I have no problem with this one because she was trying to get you fired.