On a Saturday afternoon in Manhattan, Rachel Floyd and her boyfriend Paul Isham take a shot of a dark yellow liquid called Mother F*#%in’ Fireball. “It kind of makes my leg hair follicles feel like they’re standing out,” says Isham, a 33-year-old audio visual technician whose grey hoodie is decorated with a Bernie Sanders sticker and button. Floyd, who is wearing a Feel the Bern-themed Christmas sweater, throws back the small plastic cup. “Oh man.…