Used to be extremely talkative? Rubbish! (5)
I believe the answer is:
waste
'rubbish' is the definition.
(I know that rubbish can be written as waste)
'used to be extremely talkative?' is the wordplay.
'used to be' becomes 'was' (eg 'he was...' means 'he used to be...').
'extremely' says to hollow out the word (remove centre letters) (only the extremes of the word are used).
'talkative' with its centre removed is 'te'.
'was'+'te'='WASTE'
(Other definitions for waste that I've seen before include "Spend thoughtlessly or use inefficiently" , "Become gradually weaker" , "Blow - rubbish" , "Use carelessly" , "Misuse" .)