Chronic, debilitating condition suffered exclusively by local authority staff in the UK necessitating long periods of absence from work. There are no known physical symptoms although sufferers may appear to have a sore throat/bad back/upset stomach etc. There is no known cure but the condition will usually resolve itself rapidly at the point the employee has exceeded their entitlement to paid sick leave.
Manager: Where is Mark today? Colleague: Oh he won't be in today, he always suffers from Councilitis on a Monday.