The easiest way to kill the badass cashier is to scroll over to the HF Laser Pistol, jump behind the cashier, and shoot. His gun will be too long to shoot you back, and you'll win.
Do you know what we're doing to jesus? "No" We're beating the shit out of him "Do you think I'm beating the shit out of him too?" Yes "Why" because you hate him "That makes sense to me" xD