Reaction to a bad pun (5)
(Other definitions for ouch that I've seen before include "Exclamation of pain - that hurt!" , "Cry of pain" , "Pained exclamation" , "that hurts!" , "Shout of pain" .)
'reaction to a bad pun' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for groan that I've seen before include "Sound of one in pain" , "Titus -- (Mervyn Peake)" , "Cry of pain or despair" , "Sound of pain or disapproval" , "See 18 Down" .)