The most interesting response that I've seen to Lewis's trilemma came from a psychiatric nurse. His experience of working in an psychiatric hospital was that people with delusions, such as thinking they are Napoleon, didn't seem particularly off. They were pleasant, and easy to care for. Over the course of weeks, one would get to know them. It would gradually become apparent that the delusional thinking went very deep. They really did need residential care.

So Lewis's rhetoric depends on "lunatic" connoting "raving lunatic" and there are actually four branches to his tri-lemma: liar, God, raving lunatic, some-one with serious psychiatric issues who generally holds it together and seems normal much of the time.