Why do they call it a funny bone?
Because it tingles in a very uncomfortable way when struck against an object. Often on accident. This is hilarious to everyone except the person experiencing the pain because, people are just a little bit sadistic.
It is called nicknamed the funny bone, for two reasons, the tingling sensation that you get after hitting it, and because the bone's real name is the Humerus, which is like the word humour, and therefore, funny.
The funny bone got its nickname because of that funny feeling you get after you hit it. But your funny bone isn't actually a bone at all. Running down the inside part of your elbow is a nerve called the ulnar. The ulnar nerve lets your brain know about feelings in your fourth and fifth fingers.