Crazy, out of control, nuts.
In addition to being a kind of
chair, a 'rocker' is a device that controls the
movement of a piece of machinery. When a
machine is off its rocker, it no longer works correctly.
1) You can't walk down the street in your
underwear! Are you off your rocker?
2) I'
m afraid Aunt
Betty is really off her rocker these days.