3 definitions by Sir Neville W.F.G. Mariner,

See generaly Arse Hair Demon, Klingon Arse-Pinch:

1. A medical affliction involving an infestation of microscopic gnomes with the tendency to pull one's arse-hair at will;

2. A person who is constantly nervous and jumpy is said to suffer from this malady.

N.B. A sufferer of this condition would be micro...trichotillomanic, and the chronic syndrome is micro...trichotillitis.

A longer, alternate form of this word is actually one of the lengthiest words in the English language. Sadly, it cannot be published in the UD because its length is over 40 characters, but here it is, broken-down:
From the Latin: gnomo (having to to with gnomes), ultra-microscopic (very small), perianal (surrounding the anal area), trichotillitis (condition involving hair-pulling)

Alternate form- gnomo...trichotillomania, which refers to particularly bad cases, where the gnomes are under a psychological compulsion to pull as often as possible.

The complete, obsolete, historical form of the word would be:
gnomoultramicroscopic perianal trichotillomania (spelled without the spaces).

What's with George? He jumped when I tapped him on the shoulder. It's like he has a bad case of micrognomoperianaltrichotillomania!
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The name for a sudden tug of the hair in the perianal region, often caused by the accidental shifting of an undergarment; also, to surprise someone by giving their perianal hair a tug; can refer to the cause behind a person unexpectedly yelping, or leaping to their feet, for no outwardly apparent reason.
Karen and Soneli were quietly watching TV, when Soneli leapt to her feet with a shriek, as if she had received a vigorous Klingon arse-pinch.
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Alternate spelling, "Arse-hair demon": An extremely small, gnome-like creature, with powers of invisibility, who sneaks up on unwary victims, and gives their perianal hair a sharp tug, causing them to shriek, and/or leap skyward, for no outwardly perceptible reason.
Ariel and Deanna were enjoying high tea with the Queen, when HRH suddenly gave a sharp yelp, and leapt from her seat. Royal Guardsmen rushed towards the table, but Her Majesty waved them off, stating, "Bugger off, ya sods, 'twas merely a wee arse hair demon, ticklin' me hindparts."

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