You're minding your own business, perhaps completely focused on the task at hand and it comes at you with no warning whatsoever. WHACK! You hit your Humerus Bone (AKA Funny Bone).
As I described the above scenario you probably cringed. There's nothing FUNNY about that! It hurts and it's the weirdest kind of pain, too. I think it's really called a "funny" bone (other than for the obvious reason) because it makes others laugh when they see it happen to you.
Do you ever notice how if someone gets hurt and they're not permanently damaged, that it's actually funny? You see it in movies and cartoons all the time. We laugh when someone falls and we are especially hardy in our chuckle when we see someone bonk their head on something (which I do on PLENTY of occassions). It's plain and simple funny to be goofy and out of the ordinary, no matter the scenario.
I guess, I feel that if we can get a laugh out of someone else, shouldn't we also (if not more so) get a laugh when silly things happen to us? I think so. Usually when I fall or trip or bump my noggin, instead of looking around to see if anyone (heaven forbid) "saw" the tragedy which just ocurred, I laugh. I So much more fun than being stressed.