I loved Big Fish.
The "Gentleman Liar" is a tradition in the south. I know a man who does this very thing. I really, really look forward to my occasional visits with him.
You have to understand, that the son was reacting against/not understanding the tradition. Everyone knows the Liar isn't telling a true story; he's just telling an "interesting" story. He usually sits in some semi-public place, and everyone who wants to hear the story, can sit and hear it.
Loved; absolutely loved the movie. And in the end the son finally "got it" and became a "gentleman liar" himself. Or is that "hisself"?