omg, how is this scene still being taken out of context after 10+ years? In the scene mentioned, Tidus, the protagonist of the story, is feeling depressed and Yuna, the summoner who Tidus is guarding, tries to cheer him up. One of her methods is forcing(!) yourself to laugh. It looks ridiculous, it sounds ridiculous, heck, the other characters watching the scene think it's ridiculous and even Yuna herself at some point tells Tidus he should probably stop. The laugh sounds forced, because it is. And intentionally, at that.