This has been a standby nonsense word in my household for about four years now. It's also our word for a smoothie. When my daughter was a baby and upset by the noise of the blender, we would shout booga booga while flensing the mangoes, and so it was transferred to the substance itself.
Coined by David Steinberg during a skit where he, acting the part of a zany-disturbed patient, suddenly had a notion to change the piece midstream before his partner, the "psychiatrist" entered the room. He signaled the change with the announcement "Okay, you can send in the patient, now." The partner, upon his entrance and without missing a beat became the patient and they improvised onward. Booga booga arose somewhere in the ensuing action.
I learned this listening to Michael Feldman's interview of David Steinberg on Whad'Ya Know?
I still remember the joke wherein I first heard "booga booga" and had no idea of its origin. I doubt that David Steinberg had the same connotation in mind that the joke depends on...