A phrase used in a spoof gameshow of the same name in the BBC Comedy sketch series That Mitchell and Webb Look. The 'game' makes no sense at all, and appears to involve the contestants saying random numbers, with the host periodically congratulating them for achieving some unintelligible goal by saying "That's Numberwang!" Variants include "Das ist Numbervang!" (from Episode 5's German version of the show), "That's Wangernumb!" (from the final round of each sketch) and "That's Wordwang!" (from episode 6's 'spin-off' show)
BlackMageJawa has started repeatedly linking to the sketches on YouTube and using the phrase in a vague hope that it will take off as some sort of fad.
It hasn't yet.