Blokes, great nuisance (6)
I believe the answer is:
menace
'nuisance' is the definition.
(I have seen 'serious nuisance' mean 'menace' so perhaps 'nuisance' could also mean 'menace')
'blokes great' is the wordplay.
'blokes' becomes 'men' (I've seen this in another clue).
'great' becomes 'ace' (ace can informally mean very good).
'men'+'ace'='MENACE'
(Other definitions for menace that I've seen before include "Threaten with harm or danger" , "Threat, show of hostility" , "Threat, danger" , "Act in a threatening manner" , "Harmful person" .)