when something is so ridonkulous, so that the ridonkulousness of it is multiplied by three, or, in other words, tripled. thus, it is not just ridonkulous, but TRIdonkulous. the "tri" signifies the triple nature of the ridonkulousness.
karl: shit did you see pyramid that kid made out of orangina bottles?
jay: that was ridonkulous.
karl: no man. that was beyond that. that was TRIDONKULOUS.