How about, "If I asked your twin if she is frigid, what would she say?" Assuming you want to fuck the nympho, book your session with the one who replies no.
If the frigid twin is the liar, she would reply yes because the nympho tells the truth. The nympho twin tells the truth so she would reply no.
If the frigid twin always tells the truth, then the nympho is the liar and would say yes. Etc.
I didn't google this but it's a familiar logic puzzle from other contexts (Bertrand Russell maybe?)
Originally Posted by slocum
Great answer Slocum!
That is sort of a variation of the answer I was thinking of, which is to ask "Which one of you would your sister say is the frigid one?"
They will both point to the nympho.