Arrogant fool with high-class china (8)
I believe the answer is:
assuming
'arrogant' is the definition.
(I've seen this in another clue)
'fool with high-class china' is the wordplay.
'fool' becomes 'ass' (both can mean a stupid person).
'with' says to put letters next to each other.
'high class' becomes 'U' (as in U and non-U speech).
'china' becomes 'ming' (Chinese porcelain from the Ming dynasty).
'ass'+'u'+'ming'='ASSUMING'
(Other definitions for assuming that I've seen before include "Accepting something without proof" , "Taking as true" , "Taking to be the case" , "Based on the supposition" , "Taking on - arrogant" .)