One whose ego (or attitude) is so large that their head, literally, looks fatter.

To be used as a Term of Endearment. Can also be used in exasperation.
Mary: "Who is the OG Fatty Fat Head?'
Sarah: "Umm... I'm pretty sure that's Randee Jo"
Mary: "Ooohh..."

Christina: "Stop being a Fat Head and come pick me up!"
Caitlin: " What the hell does that even mean?!? Is that even a phrase?"
Christina: "Look it up on Urban Dictionary, it's there"
by Mangofatdoody September 27, 2010
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