I remember Stone was pretty rough...but I also grew to consider it to be the taste of a strong effective kava, thereby learning to love it's horrificness. I think I'd say this heavy fiji waka I've been on lately is even worse, possibly only because it provides me with less happiness than Stone. But that's all over with tonight, as I try my 1st batch of MeloMelo.
The strangest flavor I've had is Mahakea. Can't remember from where, or how it tasted when I first got it....but when I came back to it years later, it brewed up a weird amber/brown color and had an indescribable flavor that was only vaguely reminiscent of 'typical' kava.