Ichabod

Penny calls Sheldon this, a reference to the character Ichabod Crane in the short story "The Legend of Sleepy Hollow" by Washington Irving, first published in 1820. Penny uses this name because of Sheldon's lanky build. Ichabod Crane's appearance was similar, although much exaggerated, described in the story this way:

He was tall, but exceedingly lank, with narrow shoulders, long arms and legs, hands that dangled a mile out of his sleeves, feet that might have served for shovels, and his whole frame most loosely hung together. His head was small, and flat at top, with huge ears, large green glassy eyes, and a long snipe nose, so that it looked like a weather-cock, perched upon his spindle neck, to tell which way the wind blew. To see him striding along the profile of a hill on a windy day, with his clothes bagging and fluttering about him one might have mistaken him for the genius of famine descending upon the earth, or some scarecrow eloped from a cornfield.

It seems a bit out of character for Penny to use a literary reference like this until one considers that the story and the character are well known apart from the original literature. The Legend of Sleepy Hollow has become everything from a Disney cartoon to a horror film.