Casual worker in affront showing no end of contrition (9)
I believe the answer is:
offhanded
'casual' is the definition.
(I've seen this before)
'worker in affront showing no end of contrition' is the wordplay.
'worker' becomes 'hand' (hand is a kind of worker).
'in' means one lot of letters goes inside another.
'affront' becomes 'offend' (I've seen this before).
'showing no' is a deletion indicator.
'of contrition' becomes 'ed' (I can't explain this - if you can you should believe this answer much more).
'hand' going into 'offend' is 'offenhandd'.
'offenhandd' with 'end' removed is 'offhand'.
'offhand'+'ed'='OFFHANDED'
(Other definitions for offhanded that I've seen before include "In casual or indifferent manner" , "Casual or curt in manual way?" .)