rocker

To become crazy or mentally unsound; to become extremely foolish or foolhardy. I'm going to go off my rocker if I have to hear that blasted song once more! I think Jane's grandmother has gone off her rocker lately. You must have gone off your rocker if you think that's a good idea!

Fig. crazy; silly. (*Typically: be ~; go ~.) Sometimes, Bob, I think you're off your rocker. Good grief, John. You're off your nut.

to be crazy Spending that much on a car! He must be off his rocker! (informal)

Also, off one's nut or rocker or trolley or chump . Crazy, out of one's mind, as in You're off your head if you think I'll pay your debts, or I think Jerry's gone off his nut over that car, or When she said we had to sleep in the barn we thought she was off her rocker, or The old man's been off his trolley for at least a year. The expression using head is colloquial and dates from the mid-1800s, nut has been slang for "head" since the mid-1800s; rocker, dating from the late 1800s, may allude to an elderly person falling from a rocking chair; trolley, also dating from the late 1800s, may be explained by George Ade's use of it in Artie (1896): "Any one that's got his head full of the girl proposition's liable to go off his trolley at the first curve." The last, chump, is also slang for "head" and was first recorded in 1859.

Also, off one's nut or trolley . See off one's head.

Out of one's mind; crazy.