nutter

Nutter is a British informal word for somebody thought to be mad. Blunt, and used far more often than it should be.

It is applied to reckless drivers, to strangers behaving oddly and to friends doing something daring, and in that last use it is almost admiring. As with a great many words in this family, using it about actual mental illness is unkind, and the casual use has helped keep that stigma alive. The related nut and nutty follow the same pattern. Its close cousins are loony and headcase, and all of them are best understood rather than used.