Bored of extremely forgettable party (3,2)
I believe the answer is:
fed up
'bored' is the definition.
(I've seen this before)
'extremely forgettable party' is the wordplay.
'extremely' suggests removing the centre (only the extremes of the word are used).
'party' becomes 'dup' (Democratic Unionist Party).
'forgettable' with its middle removed is 'fe'.
'fe'+'dup'='FED UP'
'of' is the link.
(Other definitions for fed up that I've seen before include "Surfeited" , "Bored - disgusted" , "Unhappy" , "Annoyed, bored" , "Disaffected" .)