You learn a lot when you work as a bartender, but the people who benefit from slinging drinks at all hours of the night aren’t just the drunks getting their buzz on. “I’ve seen so much dark shit, man” says Billy McCarthy, singer and guitarist for the Brooklyn band Pela, who release their debut Anytown Graffiti this month. “I’ve served strippers who’ve just had men slip dollars into their thongs. I’ve served cops who’ve just come from a homicide scene. Lawyers who are cheating on…