She's telling her friends go ahead and let me hear it because I know you're going to make fun of him or point out his faults in some way. Alan is the name of her new boyfriend and bashing means criticizing. Maybe she could see the looks of disapproval on their faces. Maybe she was just nervous about her friends meeting him. Or maybe he spent the whole lunch talking about crossfit. You could add bashing to other words too like telling your friend quit the [your favorite sports] team bashing.