Case of trendy attitude (8)
I believe the answer is:
instance
'case' is the definition.
(I know that case can be written as instance)
'trendy attitude' is the wordplay.
'trendy' becomes 'in' ('in' can mean fashionable).
'attitude' becomes 'stance' (stance is a kind of attitude).
'in'+'stance'='INSTANCE'
'of' acts as a link.
(Other definitions for instance that I've seen before include "Case or example from ancients" , "A case or example of something" , "Example or single occurrence of something" , "Particular case; cite" , "'Example, illustration (8)'" .)