You say Wha-Wha-Wha when there is a awkward and funny silence in a the room.Or if someone messes up on something you scream,"Wha-Wha-Wha!"It's kinda like Nelson from the Simpsons saying/making fun of the person saying,"HA HA!"
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.