An onomatopoetic phrase, when spoken aloud sounds like the two trumpet notes used on tv shows when a bad joke is told or something particularly cheesy happens. When used as a noun it describes a person who is unusually socially inept or just very dorky.
"Oh my God, here comes so-and-so, she is such a wha wha."
"She knitted her own pants and matching blazer? How does she even go out of the house looking like that? What a wha wha!"
"He walks like a vulture and breaths out of his mouth. What a wha wha."