Originally "wakka wakka wakka" as uttered by Fozzie the Bear of Muppet fame. Fozzie wanted to be a comedian. Unfortunately, he was terrible. The threefold utterance was part of Fozzie's act. The shortened version has gained usage as an expression of delight, exultation or lust (sometimes all at the same time).
Fozzie: !Ahhhhhh! Wakka-wakka-wakka! Thank YOU, thank YOU, and thank YYYYOU!!
1. 1/3 of a quote from Fozzy the Bear from the Muppets: "Wokka Wokka Wokka"
2. The sound Pacman makes as he gobbles up candy in the dark while listening to repetative electronic music and running from brightly colored incorporeal beings until he gets the EXtra special magic pill when he tries to get as close to all of them as possible, until it wears off and he has to go looking for another one.