The 'tardle shell' is the turtleshell-like tiny backpack so frequently seen on the morbidly obese and mentally challenged folks in our society.

You often see heavy set people with these backpacks, which have two straps (usually black and/or thin, corded). These straps go around the shoulders to hold the tardle shell in place in the middle of the back.

The name 'tardle shell' comes from 'turtle shell' and 'retard', since often those called 'retards' wear these backpacks like shells.

Noun: a friend who is usually only called upon by a friend when a more primary/prominent friend is unavailable.

Taken from the term “second string” in an athletic competition situation. In football, if the star quarterback gets injured during a play, the second string is called off the bench to replace him/her. A “Second String Friend” is essentially benched until needed, if ever.

Synonyms: Plan B, Second Choice, Secondary Friend, Benched Until Needed