off one's block / chump / crust / head / nut / onion

adj

mad, crazy. These phrases are all elabo-rations of the well-established colloquial-ism, 'off one's head' (heard since the mid-19th century). The terms are some-times extended to mean intoxicated by drugs or drink, more usually denoted by phrases beginning with 'out of', such as out of one's head.