We define “fun” as anything you can say “Weeee” while doing and its appropriate. Case in point, flowing a huge section at the trails definitely warrants a “Weeee”, while the cooking class your mom suggested you take over summer because it would be “fun” doesn’t really seem “Weee” appropriate. Educational maybe but if you fired out a “WEEEEE!” while mixing flour, eggs and milk, you would probably be kicked out of the class. On the flip side, “Weeee” is always BMX appropriate, hence, BMX is always fun. Very scientific, we know, but you asked.