To develop an illness or sustain an inury, possibly self inflicted, which will preclude you from work, but you can still enjoy a rich and varied social life.
Orginates from the 1914-18 War, when reluctant English soldiers would shoot themselves in the foot, to get returned to Blighty, or Great Britan, and invalided out of the Army.
Hangovers can count if passed of as food poisoning

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