Best dismissed by the party (5)
I believe the answer is:
outdo
'best' is the definition.
(I know that best can be written as outdo)
'dismissed by the party' is the wordplay.
'dismissed' becomes 'out' (I've seen this before).
'by' is a charade indicator (letters next to each other).
'the party' becomes 'do' (do is a kind of party).
'out'+'do'='OUTDO'
(Other definitions for outdo that I've seen before include "Br superior to (someone)" , "Eclipse" , "Overcome" , "Surpass someone at something" , "Perform better than, be superior to" .)