Being uncomplimentary and nettling German lady terribly (12)
I believe the answer is:
unflattering
'being uncomplimentary' is the definition.
('unflattering' can be similar in meaning to 'uncomplimentary')
'and nettling german lady terribly' is the wordplay.
I cannot quite understand how this works, but
'and' could be 'n' (common abbreviation for 'and') and 'n' is found within the answer.
'german' could be 'g' (abbreviation) and 'g' is found within the answer.
'lady' could be 'teri' and 'teri' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for unflattering that I've seen is " Not kind (to one's appearance)".)