Definitely trustworthiness. If you can trust that person then you can totally relax and enjoy their humour,looks,wit,charm,confidence and sexiness. Without the first, you will never be at ease to enjoy anything.
Well, if they can say something bright enough or funny enough to break the mesmirized state of drool that falls upon me and sets me into my animal stupor while they are being nude, I can conclude they may be both smart and nude. There are also oppportunities for proving smartness after, uh, nudity finds a brief lull in its appeal, but I will confess these are more difficult to capitalize on as many men are asleep at that point.