What does bantha fodder mean?

You are obviously a Star Wars fan. Fodder is what you feed to an animal. A Bantha is an animal that was thought up for in Star Wars. When someone tells another person that they are any kind of fodder, they are saying that there will be nothing left but enough to feed whatever animal is being referenced. Or if it is an herbivore, they are going to be used to fertilize the plants that are used to feed that animal. Basically, it's like saying "I'm going to kick your kiester!"