Being A Billy, or a Billy Head, is basically acting like a Billy-Goat, like the animal. Literally a jack-ass, or ass-hole. Douche-bag is also accepted. The animals are rather stupid, and purposeless.
This is not a joke, there are people who use this word(s), mainly up in the mountain regions, where Billy Goats are found.
plain Billy, depending on the wording.
Examples: You damn Billy. You such a Billy, you fuck-tard. Or my favorite, Don't be Billy, or Don't be Billy you stupid Fuck.
2) someone who destroys things because he/she thinks that people are impressed/ intimidated by it.
2)Scott came in, being a Billy Badass as usual, and kicked over the fuckin couch.
person #2 "yeah man don't be a billy"