Solipsists of the world, Unite! You have nothing to lose but your Existence!·
C, the proposition is logically tenable but humanly provides a very tenuous (not to say treacherous) footing for real living. It is one of those things that takes infinite steps to disprove and therefore gets very attractive to sophomores who want to impress ladies on campus. I can guarantee you if you go around and condemn all your friends to the status of figments, they'll find friends more ready to believe in them reciprocally. It's much nicer that way -- here...I'll believe in your figment, and you can believe in mine!