Regretted looking angry about the socially uppish (4)
I believe the answer is:
rued
'regretted' is the definition.
('rue' can be a synonym of 'regret')
'looking angry about the socially uppish' is the wordplay.
'looking angry' becomes 'red' (someone may go red when angry).
'about' indicates putting letters inside.
'the socially uppish' becomes 'u' (I can't explain this - if you can you should believe this answer much more).
'red' enclosing 'u' is 'RUED'.
Can you help me to learn more?
(Other definitions for rued that I've seen before include "Was contrite about" , "was remorseful" , "Bitterly regretted" , "'Regretted, repented (4)'" , "Was sorry" .)