Having had too much of a fatheaded misguided dupe (3,2)
I believe the answer is:
fed up
'having had too much' is the definition.
I can't tell whether this defines the answer.
'fatheaded misguided dupe' is the wordplay.
'fatheaded' becomes 'f' (this might be a standard abbreviation of which I'm unaware).
'misguided' is an anagram indicator (letters guided into the wrong places).
'dupe' with letters rearranged gives 'edup'.
'f'+'edup'='FED UP'
'of a' is the link.
Can you help me to learn more?
(Other definitions for fed up that I've seen before include "Annoyed, bored" , "Bored - disgusted" , "Informally bored or discontented (3,2)" , "Surfeited" , "Fattened - annoyed" .)