What is the correct way to eat a muffin?

The proper way to eat a muffin is the same as any sort of bread or toast. You put it on your plate, and put with your butter knife a small amount of spread you wish to use (if any) onto your bread plate near the muffin.

Then you tear off a small mouthful of the muffin, butter only that piece, and place it in your mouth with your thumb and index finger. And repeat.