Will is kind of a negative guy - he says "no" a lot more than he says "yes". Much to Mom's chagrin, I like to challenge him and get into playful yes-no arguments. Mom doesn't like this because then when we have to be definite and tell him "yes, you are doing this" or "no, you cannot do that" - then he doesn't take us as seriously. And she's right, but I can't help myself.
Anyway, Will took things to a new level when he discovered he could emphasize his 'nos' as "NO WAY".