Employer sure to get upset (4)
I believe the answer is:
user
'employer' is the definition.
(someone who employs or uses something)
'sure to get upset' is the wordplay.
'to get upset' indicates anagramming the letters (I've seen 'getting upset' mean this).
'sure' with letters rearranged gives 'USER'.
(Other definitions for user that I've seen before include "Maybe one needing pot" , "Person who takes drugs" , "Person taking drugs" , "Consumer" , "One operating something" .)