You dumbed down your writing cause it was too proffesional? That says it all, honestly.
I've used that argument in the past three applications because it's such a poignant point. It sounds kind of arrogant to put it that way (which I know I did in the application) but there was no other way of putting it aside from typing more "casually" or something. In the end, if I remember his issue correctly, it was a case of RDM that he wouldn't let me handle because I was typing like I had a stick up my ass (too "professionally"), basically.