Social ineptitude could make you ultimately cagier, eh? (9)
I believe the answer is:
gaucherie
'social ineptitude' is the definition.
(gauche can mean socially inept)
'make you ultimately cagier eh?' is the wordplay.
'make' is an anagram indicator.
'ultimately' says to take the final letters.
The final letter of 'you' is 'u'.
'u'+'cagier'+'eh'='ucagiereh'
'ucagiereh' is an anagram of 'GAUCHERIE'.
'could' acts as a link.
(Other definitions for gaucherie that I've seen before include "Slip" , "Awkwardness" , "Socially awkward acts - huge Erica (anag)" , "Tactless behaviour" , "clumsy behaviour" .)