"I want to shut them down with a effective remark and be on my way. Get what I mean?" Yes. You want to shut them down with an effective remark and be on your way.
Okay, tell them that unless they apologize you will punch them in the face. Or another approach could be: if you don't know the person walk away. If you do know the person then tell them they are dead to you and walk away.
If you are after some bon mot that will stun them back to their senses and leave them speechless, mouths agape, as they watch you saunter away.. that's not going to happen. They are liars and engaging a liar with reason is like bringing an Eskimo kiss to a gun fight.