Derived from the combination of the words moe and diabetes, moebetes is an emotional condition in which anime fans are exposed to such great amounts of moe cuteness that they end up with constantly high moe levels, similar to how a diabetic has high blood sugar.
Similarly, one who suffers from (if you can call it suffering) moebetes is identified as a moebetic
"Hello, I'm Wilford Brimley, and I have moebetes"
--Wilford Brimley, shortly after watching the first two seasons of K-on! back to back