A misnomer used to make McDonald's sound like an upscale eatery. Similar to pronouncing Target as Tarjay, it gives the speaker an air of superiority while also almost definitely proving they are a corny dad. The Ronnie Mac in question is, of course, Ronald McDonald.
When your lips are so dried and chapped the skin above your upper lip and below your lower lip becomes red and inflamed. Your lips look like Ronald McDonald's.
"Holy cow! Look at her lips; she has Ronnie Syndrome."
Julie: "Hey Ronnie, how's it going?"
Michelle: "Stop calling me Ronnie. It will be gone by spring."