Manner of a non-drinker, irritable, testy, initially, rude losing head (8)
I believe the answer is:
attitude
'manner' is the definition.
(thesaurus)
'a non-drinker irritable testy initially rude losing head' is the wordplay.
'non drinker' becomes 'tt' (Teetotaller abbreviation).
'initially' indicates taking the first letters.
'losing head' means to remove the first letter.
The first letters of 'irritable testy' is 'it'.
'rude' with its first letter removed is 'ude'.
'a'+'tt'+'it'+'ude'='ATTITUDE'
'of' acts as a link.
(Other definitions for attitude that I've seen before include "Carriage - outlook" , "Way of thinking or behaving" , "Truculent behaviour" , "Position or mental approach" , "Manner" .)