What part of the body is sometimes called the funny bone?

Answer:

The humerus, which is the upper arm bone, is sometimes called the funny bone but, strictly speaking, this is not correct.

In reality, the "funny bone" is not the bone at all, nor even the elbow, but the ulnar nerve at the end of the humerus where it meets the elbow. The ulnar nerve is the nerve that runs near the ulna bone of the lower arm. It is the nerve that sends messages to your brain about sensations in your fourth and fifth fingers. It's also one of the nerves that controls some movement of your hand.
When this ulnar nerve is jolted or bumped against the end of the humerus, it creates the odd tingling sensation which has given rise to the term "funny bone".