Tantrum shown by office worker about over (6)
I believe the answer is:
temper
'tantrum' is the definition.
(I've seen this before)
'shown by office worker about over' is the wordplay.
'shown by' is a charade indicator (letters next to each other).
'office worker' becomes 'temp' (I've seen this before).
'about' is a reversal indicator.
'over' becomes 're'.
're' backwards is 'er'.
'temp' next to 'er' is 'TEMPER'.
(Other definitions for temper that I've seen before include "Harden metal by heating and cooling" , "Tantrum" , "bait" , "State of mind as regards anger (6)" , "Mood (often bad)" .)