You’re standing at a crossroads next to a guy who always tells the truth. A third person comes up to you guys and wants to know which road to take, but doesn’t know which one of you is which. What should he ask?
Why is a raven like a writing desk?
Getting a bunch of them together is an unkindness.
Damn, I was hoping the OP would field all questions with some great wild claims and a wink in the eye.
What did you expect from a liar?
They both have inky quills. Duh.
Cecil! Is that you?
No. It’s a guy I used to know named Paul. Just watch him deny it. 
Did you ever see the first two years of the sitcom “Newhart” (the one when he’s in Vermont)
Dick Loudan has a neighbor Kirk who runs the cafe next to the inn and he’s a pathological liar. Real funny stuff.
How did you enjoy being married to me? It wasn’t so good for me, frankly.
Did you shoot a man in Reno, just to watch him die?