This is what you say when you cannot enunciate the phrase "have a good one". There are a couple of town's named Kill Buck and Salamanca where honky's will use the the phrase habba-goob-un because they struggle to speak basic English.
When you are telling someone goodbye: "Habba-Goob-Un!!"
Boys who enjoy yaoi (a genre in Japan that contains sexual and/or romantic relations between two men); literally translates to "rotten boy"; corresponding female : fujoshi