Green’s Dictionary of Slang

(US) clumsy.

1976

R. Daley To Kill a Cop 93: Nearly all of [the alarms] every morning were set off by accident by left-footed bank officials.

(N.Z. prison) to pass information to the prison authorities in the hope of enjoying an easier life.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 106/2: left hand drop v. to secretly pass information to prison authorities in an attempt to curry favour and get through one’s sentence more easily.

of sexual relations, parenthood: extra-marital, illegitimate.

1877

H. Hartigan Stray Leaves (1st ser.) 45: There was a legend in the regiment that he was the son, ‘on the left side of the blanket,’ of some great land-owner.