A Billy, or Billy-Headed. Also Billy-goat.
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.
Examples: Hey don't be like a Billy. Man your so fucking Billy Headed. In some cases it can be sub-divided down to just
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.