The fandom went apestuff on her misplaced eye
episode one, when her character first appeared, the error was there and 4chan thought it was funny
they gave her a name for the hell of it.
they weren't being serious. Derpy Hooves? come on. people took it onward from there, because why not? it's not an official character with a set-in-stone personality. creativity steps in. plus, they were bored waiting for part 2
which was probably not even her since her mouth stopped moving and the word continued
this isn't real people, it's an animation
lip synchronization is rarely that accurate. plus, it was episode 4. very beginning, still getting into the swing of things.
she was the one who said muffins. watching the very quick scene makes it blatantly obvious. the fun part though is she didn't have the eye error. background characters have a little number placed by storyboard artists, it tells the animators who to put in which scenes, and she was "lucky" enough to be the one placed there.
she suddenly became a chronic muffin addict and everyone has to include her lazy eye and a loving muffin.
every person interrupts her differently. some make her enjoy muffins, obsess over muffins, or no muffins at all. mailmare, mother, doctor who partner, or just a simple pegasus. even with her eye. some artists don't add the lazy eye. she isn't any of these things, people essentially make her whatever they want her to be.
no one
has to do it. they choose to do it. i never see anyone get bullied for not including that one characteristic.