Regret insult in speech? Rubbish! (7)
I believe the answer is:
rhubarb
'rubbish' is the definition.
(rhubarb can mean nonsense or rubbish)
'regret insult in speech?' is the wordplay.
'regret' becomes 'rue' (to rue something is to regret it).
'insult' becomes 'barb' (I've seen this before).
'in speech?' shows a homophone (sound like) (I've seen 'in speech' mean this).
'rue'+'barb'='ruebarb'
'ruebarb' sounds like 'RHUBARB'.
(Other definitions for rhubarb that I've seen before include "Edible red-stalk plant" , "murmurings in the theatre" , "extra speech?" , "In America, heated dispute" , "Reddish, fleshy-stalked plant, makes nice tart" .)