Arrogant yuppy regularly lacking compassion (6)
I believe the answer is:
uppity
'arrogant' is the definition.
(thesaurus)
'yuppy regularly lacking compassion' is the wordplay.
'regularly lacking' means one should take alternating letters.
'compassion' becomes 'pity' (pity is a kind of compassion).
The alternate letters of 'yuppy' are 'up'.
'up'+'pity'='UPPITY'
(Other definitions for uppity that I've seen before include "Presumptuously arrogant" , "Snobbish" , "Cheeky or presumptuous" , "Bumptious" , "Full of oneself" .)