Who knew Wikipedia could be so straight-faced when ending an entry with a bir of levity?
Witzelsucht, from the German witzeln, meaning to joke or wisecrack, and sucht meaning addiction or yearning, is a set of rare neurological symptoms characterized by the patient’s uncontrollable tendency to make puns, tell inappropriate jokes and pointless or irrelevant stories at inconvenient moments. The patient nevertheless finds these utterances intensely amusing. It is associated with small lesions of the orbitofrontal cortex.
It is distinguished from pathologic laughing by virtue of congruent affective experience and expression, and an admixture of irritability and mirth. It is most commonly seen in patients with frontal lobe disease or injury, particularly right frontal lobe tumors or trauma. Elderly people are very pron to this disorder because of the decreased mass of their gray tissue, for instance the stereotype of the wise-cracking grandfather may have originated from as it became a comon part of every day life. Larry king is said to have this disorder but refuses to be tested. [Italics mine]
Quick show of hands: who knows someone with this unfortunate yet very annoying disorder?
Thanks to NPR’s radio show Wait, Wait, Don’t Tell Me! Sunday, Nove 21, 2010, and to Wikipedia.org
 Mendez, M.D., Ph.D, Mario F (2005). Moria and Witzelsucht from Frontotemporal Dementia. The Journal of Neuropsychiatry and clinical neurosciences.