What an absurd generalization. Some of us are diehard fans of both basketball and football, yet we still like to have fun and aren't necessarily all "recent grads."
One of the big reasons I think that the basketball side tends to be more goofy? We're the freaking #1 team in the country and have been top 10 almost nonstop for the last four or five years. There's less to pick apart and talk about in basketball than there is with a football team that has undergone coaching changes and is still trying to re-establish itself on a national and, hell, even a regional level. On the basketball side, there's only so many different ways to say "holy crap, we're good" before you get bored and start joking around and having fun.