1
general::
1. A point on the elbow where the ulnar nerve runs close to the surface and produces a sharp tingling sensation when knocked against the bone. For example, Ouch! I just banged my funny bone. The expression is a pun on humerus (pronounced the same as humorous), the Latin name for the long bone of the arm. [Early 1800s] 2. A sense of humor, as in That comedian really tickles my funny bone. This expression is derived from def. 1.
American Heritage Idioms
2
general::
Phrase(s): funny bone [and] crazy bone
a spot near the elbow bone that is very sensitive to the touch. • Ouch, I hit my funny bone. • Effie bumped her crazy bone and made a horrendous face.
McGrawhill's American Idioms And Phrasal Verbs