Mocking father over in seedy bar (8)
I believe the answer is:
derisive
'mocking' is the definition.
('derisive' can be a synonym of 'mocking')
'father over in seedy bar' is the wordplay.
'father' becomes 'sire' ('sire' can be a synonym of 'father').
'over' shows that the letters should be reversed in order.
'in' means one lot of letters goes inside another.
'seedy bar' becomes 'dive' (I've seen this before).
'sire' written backwards gives 'eris'.
'eris' inserted inside 'dive' is 'DERISIVE'.
(Other definitions for derisive that I've seen before include "'Scornful, mocking (8)'" , "Taunting" , "Contemptuous" , "Expressing contempt" .)