There's a ton of funny quotes in the game. One I recall is when you battle one of those Behemoths and wakka says something like "I wonder how many steaks you can make with that!"

Or in Guadosalam when you speak with LULU after visiting the Farplane.
If you choose "you're more my type Lulu" as Tidus' response, Lulu responds "Interesting, I guess I'll add you to my list. I wish you good luck little boy, you're gonna need it!"