Signitus

One of those socially incapacitating ailments forensically listed, or at least embalmed, by the Guild of Barber-Surgeons in their indispensable medical manual Household Medicine, Hair-Care and Simple Surgery.

Signitus is the condition where a normal citizen of Ankh-Morpork is inclined to run away, at speed and in a state of horror, from anyone holding more than three books. Treatment is medicinal brandy administered orally. If this does not work, up the dose.