I can't claim in-tact virginity in these matters -- I used to watch Married With Children, which I think was the opening salvo of upstart FOX in cracking the mainstream sitcom lineups by trying to elevate tastelessness to art. It did make me laugh.
But I still don't know where "bwaaaahaahaa" comes from or exactly what it means.
“bwaaaahaahaa” is an ominous, sinister and or accentuated laugh....kind’a. ;o)