Someone who resembles a heavier Matt Damon and hits on women in Public.
The only way to defend against a Fat Damon is to address everyone in the vicinity, and in the most retarded voice possible proclaim, "Faaaaat Daaaamon".
Guy1: "Hey buddy, you better keep an eye on your girl. Looks like she's getting Fat Damoned at the bar."
Guy2: Approaches the bar gaining the attention of all around and proclaims in a retarded voice, "Faaaaaat Daaaaamon."
an insult towards fat people. the humor of the term gets its punch because it rhymes with actor Matt Damon.
Doug: Carrie! You ARE abusive towards me! You make fun of my weight all the time!
Carrie: I do not!
Doug: Oh yeah? What about the time you called me Fat Damon? That was five minutes ago!!