Annoying lip-smacking?

How can I kindly tell my parents and close friends to please not smack their lips without sounding snooty? It is one of my biggest annoyances but whenever I ask my mom to stop, she just gets quiet and stops looking at me. I don't want to embarrass people, but I can barely stand to eat or be around others that make noises like that. It makes me want to cringe and pull my hair out!