1. The instance of the anus (or ass) achieving a vacuum effect. In outer space, it is the black hole; in humans, it is the anus. It is the moment usually after a fart is expelled, the ass inhales air-- thus creating a vacuum effect. With practice, one can continue farting for minutes at a time through circular breathing (inhaling and exhaling) through the anus; best achieved while bent over on all fours, and relaxed. One may find extreme discomfort while the ass vacuum effect occurs while swimming.
2. A phrase used to express a moment of disappointment or even happiness by abrupt exclamation. Commonly used with a short, inward slurping sound made by the mouth, following the phrase to declare and enhance random/nastiness.
3. A statement similar to that of "EUREKA!" or of the same nature as having an epiphany or great idea; one could say "ass vacuum" in a very calm tone of voice or even a subtle whisper said near friends or strangers to cause them confusion or be interested in what you have to say.
4. A mediocre but effective derogatory ...