Oversensitive and extremely testy, bearing pained expression (6)
I believe the answer is:
touchy
'oversensitive' is the definition.
(thesaurus)
'extremely testy bearing pained expression' is the wordplay.
'extremely' says to hollow out the word (remove centre letters).
'bearing' is an insertion indicator.
'pained expression' becomes 'ouch' (I've seen this before).
'testy' with its middle removed is 'ty'.
'ty' going around 'ouch' is 'TOUCHY'.
'and' acts as a link.
(Other definitions for touchy that I've seen before include "Thin-skinned, easily offended" , "Ticklish" , "Quick-tempered" , "Irritable" , "Quick to take offence" .)