off

   1. American

   to kill

   Perhaps a shortened form of bump 5 (OFF ):

    Maybe he stiffed the waiter and the guy followed him down here and offed him. (Sanders, 1973)

   To off yourself is to commit suicide:

    I just don't want to off myself like so many cops do. (Wambaugh, 1975)

   2. with its implications of departure and decay precedes many phrases indicating types of mental illness as follows:

    Off at the side, of a mild condition, is obsolete: Not 'all there' — 'off at the side'. (Linton, 1866)

   Off your head covers anything from a temporary forgetfulness to lunacy, with many slang variants for head, such as chump, gourd, napper, nut, onion, and turnip:

    I must be going off my chump. (Wodehouse, 1930)

    He feared she had gone off her gourd, and he was scared. (Sanders, 1982)

    The fixture was scratched owing to events occurring which convinced the old boy I was off my napper. (Wodehouse, 1930)

    When... she informed him one day that she was engaged... he went right off his onion. (Wodehouse, 1922)

    Unless he had gone off his turnip, I suppose, (le Carré, 1980 — the victim had not lost his appetite)

   Another group of phrases comes from disabled transport, with the vehicle figuratively leaving the rails, its tree (or axle), or the rocker or trolley which picks up the overhead electric supply of a tram or trolley-bus:

    ... a very unstable personality placed in this environment would go off the rails. {Macleans Magazine, 9 November 1993)

    Who the hell is she? She's off her tree, (le Carré, 1989)

    I think he was really off his rocker for a bit. (Amis, 1988)

    There are moments when I wonder if I'm tipping off my trolley. (Deighton, 1985)

   The American off the wall, from the unpredictable bounce off the fence in baseball, can be used of mental illness or figuratively:

    ... it was a crazy cackle, and maybe she really was off the wall. (Sanders, 1982)

    It's bizarre. Oil nuts? A processing plant? It's off the wall. (O'Hanlon, 1996)