Barry is essentially using Bill’s love of sci-fi to hurt Bill. Jabba the Hutt is a
Star Wars villain whose image has become shorthand for obesity. So the very thing that got Bill this certificate in the first place (his love of sci-fi) is now being used to tear him down. Ishmael knows what, in theory, he should do: go to Mr. Barker and report this instance of bullying. But Bill believes that telling Mr. Barker is just going to make things worse for him—at this point, it seems safer to ignore Barry.