Upset, not working? Stop working (6)
I believe the answer is:
offend
'upset' is the definition.
(offend can mean to upset or insult)
'not working? stop working' is the wordplay.
'not working?' becomes 'off' (switched off).
'stop working' becomes 'end' (I can't justify this - if you can you should believe this answer much more).
'off'+'end'='OFFEND'
Can you help me to learn more?
(Other definitions for offend that I've seen before include "Do wrong or cause resentment" , "Act in disregard of the law" , "Wound (one's) feelings" , "Be disagreeable to" , "Cause displeasure or hurt, be nasty towards" .)