THE Oxford Dictionary’s definition of ‘pathnognomonic’: adjective, Medicine * of a sign or symptom specifically characteristic or indicative of a particularly disease or condition.

I just had to check after seeing Bad Science writer Ben Goldacre deliver his assessment of Holborn and St Pancras MP Frank Dobson to more than a quarter of a million Twitter followers last night: 

My MP, Frank Dobson, has never once replied to an email from me. In my view, this behaviour is pathognomonic of being a complacent knob end.

— ben goldacre (@bengoldacre) April 10, 2013