(See also UNCONVENTIONALITY.)

barmy on the crumpet Eccentric; a bit daft; wacko. This picturesque British expression plays on barmy ‘balmy, foolish’ and barmy ‘yeasty’—a crumpet being a breadlike muffin, here metaphorically standing for one’s head.

have a moonflaw in the brain To be a lunatic; to behave in a very bizarre or peculiar manner. A moonflaw is an abnormality or idiosyncrasy ascribed to lunar influence. This now obsolete expression appeared in Brome’s Queen and Concubine (1652):

have a screw loose To be eccentric, crotchety, or neurotic; to be irregular or amiss. As early as 1884, the phrase loose screw was used figuratively to apply to a flawed condition or state of affairs.

A more recent and increasingly common figurative meaning applies have a screw loose to states of mind or mental health. This slang meaning is used in regard to whimsical, unusual behavior rather than to disturbed or sick behavior, although the phrase tends to conjure up images of “falling apart” or “breaking down.” A British variant is have a tile loose.

have bats in one’s belfry To be eccentric, bizarre, crazy, daft. The erratic flight of bats in bell towers interferes with the proper ringing and tone of the bells, just as crazy notions darting about one’s brain weaken its ability to function. The slang term batty is a derivative of this phrase, which appeared as early as 1901 in a novel of G. W. Peck:

The analogy between sanity and finely tuned bells is an old one; its most famous expression is in Ophelia’s description of the “mad” Hamlet:

off one’s trolley Crazy, demented; in a confused or befuddled state of mind; ill-advised; senile. This expression alludes to the once-common spectacle of a motorman’s attempts to realign the contact wheel of a trolley car with the overhead wire. Since this contact wheel is also called a “trolley,” off one’s trolley may refer either to the conductor’s actions or to the fact that when the wires are “off the trolley,” the vehicle no longer receives an electric current and is, therefore, rendered inoperative.

A similar expression is slip one’s trolley ‘to become demented.’ In the more widely used variation, off one’s rocker, rocker is most often said to refer to the curved piece of wood on which a cradle or chair rocks. But since both off one’s trolley and off one’s rocker became popular about the time streetcars were installed in major American cities, and since rocker, like trolley, also means the wheel or runner that makes contact with an overhead electricity supply, it is more likely that the rocker of the expression carries this latter meaning.

queer in the attic Eccentric or feebleminded; intoxicated. In this expression, attic carries its British slang meaning of ‘the mind’; thus, this colloquialism alludes to stupidity, insanity, or drunkenness, all of which may generate bizarre behavior.

round the bend Insane, crazy. In this British expression, bend describes one’s mental faculties as being ‘out of alignment, bent, or out of kilter.’

Related expressions are go round the bend and be driven round the bend.