off one's head
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off (one's) head
1. Crazy, insane, or eccentric. Often used humorously or sarcastically. I think you're off your head for changing careers this late in life, but, hey, follow your dreams. He's off his head if he thinks he can get that engine fixed by this weekend. My auntie likes to let people think she's off her head, but she's actually incredibly clever and witty.
2. Severely intoxicated by alcohol or drugs. No wonder he's failing—he's off his head damn near every night! We all popped the pills and were off our heads by the time the concert started.
off one's head
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.