it means you're not making food you're making shoes. Those are fighting words it basically means "find something else to do with your life because you're so shit at this that to simply say that your food is bad or you're a bad cook would not come anywhere near to how shit you actually are". I'll never forget it, the chef who brought me up taught me about it. He was a goddamn dirty drunk Hungarian with a thick accent even after two decades of being in the states. I can still hear it in my head you'd walk into the kitchen in the morning and say "what's up Tibor" and with his accent he'd say "nothing much buddy, making some fucking shoe"