The expression, "BWAH-Ha-hahahahahaaaaaaaa!" and its many variations is one that is uttered most often by individuals who haven't a clue to its origins.
Started in the early 1800s by settlers racing across the North American plains in covered wagons, the expression or "sound" was originally used to mean "I'm gaining on everybody", meaning that one family and its wagon had gotten ahead of the others.
This was of course a rather silly notion, given that any settlers who actually separated from the others were sure to die without the support of the wagon train.
Everybody seemingly knew this except that one guy whipping his oxen on, yelling "BWAH-Ha-hahahahahaaaaaaaa!" as he pounded forward into oblivion and almost certain death.
Interestingly enough, this is also when and where the term "clueless" was first put into common use, having to do of course with the those who were screaming "BWAH-Ha-hahahahahaaaaaaaa!" above the pounding of oxen hooves as they withered from view and from the safety of the wagon train.
Of course some of these idiots did return, chastened and chagrined, and had to put up with the sidelong glances (and yes, snickers), from the rest of the settlers for the duration of the journey.