Okay, I suppose after years of using that reference on the various iterations of these pages it probably ought to be explained at least once. It's inherently anticlimactic -- its main purpose is to attact incredulous or uncomprehending attention for short periods. A secondary purpose is to foment indignation in a smaller group of people who know it's directed at them, but are equally unaware of what it means.
It doesn't mean anything. Actually, it means nothing specific. "Bongle" is from the Bumble Ball, a kid's toy sold sparsely across most of the US (the migration from 'Bumble' to 'Bongle' is largely a process brought on by being amused by something, then forgetting it for six months, then remembering, inaccurately, in an unrelated context.) Essentially a Bumble Ball is a normal ball with a bunch of multicolored knlbby bits all over it, and a motor & battery inside. Turn on the motor, and it wobbles around, vibrates, etc (the motor and battery assembly is mounted off-center about a central axle.) The song about the "marvelous little toy" ("... it went zip when it moved, and pop when it stopped, and whirrr when it stood still") comes to mind. Bumble Balls have a following in a similar fashion to the way that spam, rubber squids or elaborate comical jello creations do, albeit I believe on a smaller scale. The uses for Bumble Balls are numerous, as toys for kittens, actual children (the intended audience, AFAIK), etc. The use that gets most of the attention is its application as a sex toy, inasmuch as it's a wobbly vibrating cute thing that makes you laugh, and as such in some people's minds ideal for depositing in the undergarments of a suitable (usually female) sub at BDSM parties, or other such occasions where both sufficient imagination and sufficient sexual nonuptightness meet with the sort of personalities that enjoy unplanned forays to wal-mart-like stores at small hours of the morning.
The "Bunny" part is a bit simpler, merely a reference to the sexual connotation of rabbits, and of the term "bunny" in particular when applied to humans concerning their sexual proclivities, or lack thereof. "Boffing like bunnies" is an expression I came across my first year in college (this was arund 1993; I think the term had been out of fashion for awhile, or else I'd simply been out of touch); if it's taken in the sense of lighthearted cuteness, it's amusing, which is roughly what I had in mind.
Running the two together, we have the sort of term you might apply to imaginative, sexually profligate and mischevious couples; sort of like Arthur and Fenchurch in So Long and Thanks for All the Fish, but playing that role and simultaneously the role of the "couples [who] got so excited by the general wonderfulness of it all that they had to pop inside for an hour." The abstract conception of a giggly often-sexual person, mixed with the notion of a sexually-laden wobbly vibrating comical plastic kid's toy, gives the sort of description you can apply to someone, who will spend a long time being vexed about it because the odds are, without a long-winded explanation like this, that they'll never figure it out.
I've applied it to perhaps three people since making up the term. One was my now-SO (usage one), relating to when she was dating an intelligent, creative and infinitely depressive sort of individual who resembles, behaviorally, a Bumble Ball (usage two) with dead batteries, that gets blown around by the wind now and then. It didn't last long, but while she was dating him a Bumble Ball wasn't too bad a representation of her outward behavior. The third is now my assistant, but it was used mostly as one of a great many ways to make jokes about his romantic history at his expense.