I've read something like this on the net once and thought I'd share the idea
Ask: "If I told you I'm a trained psychologist who was sent to test your qualifications, how would that make you feel?" When he/she answers, take out a piece of paper and scribble furiously.
After the therapist asks you something personal, point at him/her and immitate Paul Vitti "you're good. I see where you're goin' doc.. you're good, you."
Refuse to pay unless he/she can guess what you're thinking.
Carry a small ballon filled with water in your pants pocket, and when the therapist asks you something personal, after you answer, pop the balloon. Try to have this look on your face.