Rank old fellow, 5, clutching nuts (9)
I believe the answer is:
offensive
'rank' is the definition.
('offensive' can be similar in meaning to 'rank')
'old fellow 5 clutching nuts' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'fellow' becomes 'f' (abbreviation - of a society etc.).
'5' becomes 'five' ('five' can be a synonym of '5').
'clutching' is an insertion indicator.
'nuts' becomes 'ens' ('en' can be a synonym of 'nut'**).
'five' going around 'ens' is 'fensive'.
'o'+'f'+'fensive'='OFFENSIVE'
(Other definitions for offensive that I've seen before include "nasty in another part of speech" , "Causing resentment or upset" , "Military attack" , "Insulting or repulsive" , "Insulting like aggressive attack" .)