Irritable person, sensible, not coming forward (8)
I believe the answer is:
crabwise
'not coming forward' is the definition.
(to move crabwise is to move sideways like a crab)
'irritable person sensible' is the wordplay.
'irritable person' becomes 'crab'.
'sensible' becomes 'wise'.
'crab'+'wise'='CRABWISE'
(Other definitions for crabwise that I've seen before include "to one side?" , "not in a straightforward way" , "(Of movement) sideways" .)