Someone who thinks they're your best friend when you really can't stand them; someone overly eager, almost crazily worshiping the ground you walk upon; can also be a stalker.
Sometimes they can be people who tell you how amazing you are, but still like to point out every single flaw and then add something like, "But I still love you" or "But you're still absolutely gorgeous!"
Someone socially retarded.
Also can be referred to as autogoober
or a really obnoxious kid
The most annoying about moonpies is when they say "I love you," especially if you say "I love you too" automatically.