Not reliable at work and insufferable (11)
I believe the answer is:
intolerable
'insufferable' is the definition.
('intolerable' can be similar in meaning to 'insufferable')
'not reliable at work' is the wordplay.
'at work' indicates an anagram.
'not'+'reliable'='notreliable'
'notreliable' anagrammed gives 'INTOLERABLE'.
'and' acts as a link.
(Other definitions for intolerable that I've seen before include "Unable to be endured" , "Unbearable" , "The last straw" .)