Turned up, extremely disappointed by trendy golf course (7)
I believe the answer is:
pudding
'course' is the definition.
(course of a meal)
'turned up extremely disappointed by trendy golf' is the wordplay.
'turned' shows that the letters should be reversed in order.
'extremely' means to remove the middle letters (only the extremes of the word are used).
'by' means one lot of letters go next to another.
'trendy' becomes 'in' ('in' can mean fashionable).
'golf' becomes 'g' (phonetic alphabet: alpha, bravo, charlie etc.).
'disappointed' with its centre removed is 'dd'.
'up' written backwards gives 'pu'.
'pu'+'dd'+'in'+'g'='PUDDING'
(Other definitions for pudding that I've seen before include "Fool, perhaps" , "Pease - -" , "Dessert course" , "Type of cooked food or dessert" , "Sweet course" .)