1. Commonly used as an insult among teenage boys.
2. To flubbergust is to place something edible, into a females vagina, have sexual intercourse with the item in the vagina, and after orgasm, eating the edible materials out of the vagina using your face.
3. A mildly painful, yet rewarding method of "freak sex" exploiting a woman's vagina with foreign items which are later eaten directly our of her by the partner.
Here's a fubberguster situation, where Joe is the flubberguster.
Joe has a cup of apple sauce. He pours it into Jane's vagina.