I used to work in an office with two people who were annoyingly effusive. They greeted everybody like a long-lost relative, which got on my nerves until I realized that it was either meaningless, or ironic. It was just noise they enjoyed making, and it probably made some people feel good. After that I got a kick out of it.
But the best part was when these two greeted each other! It was like the Godzilla vs. Megalon of facile insincerity! It was like a reunion of twins who'd been in solitary confinement on different continents for a thousand years! I damn near fell off my chair every time. It was infinitely better than TV.
They were serious about their insincerity, and that made all the difference.