[Liberty Valance]

OK.
http://images.google.com/images?q=%22bwahahaha%22+&gbv=2&ndsp=20&svnum=10&hl=en&start=0&sa=N

[SergeiRachmaninov]

I am aware that Google is my friend and would have resolved my question long ago by that means. Unfortunately, spelling variations -- of which there are an infinite number -- yield different, large sets of hits, because lots of people say this now.

But just as "yada yada yada" has always been with us, it only became extremely popular after they started saying it on Seinfeld.

I don't believe you KNOW the genesis of this expression in contemporary pop culture, but thanks for playing. And to you: BWAAAHAAHAA