What is the main reason when someone is funny?

Pseudobulbar affect (PBA) is a condition that's characterized by episodes of sudden uncontrollable and inappropriate laughing or crying. Pseudobulbar affect typically occurs in people with certain neurological conditions or injuries, which might affect the way the brain controls emotion.

Explanation:

The thing that makes a person Funny, is their timing. Even if the person just says 2 words depending on how they say them, and the time in comparison to the original ststement makes them funny. Or maybe even the goofy way they talk, like if they do little accents when they talk. It aldepends on your relationship with that person on what makes them funny.