Boor, just starting, you are hearing out, obnoxious (5)
I believe the answer is:
yahoo
'boor' is the definition.
(thesaurus)
'just starting you are hearing out obnoxious' is the wordplay.
'just starting' says to take the initial letters.
The first letters of 'you are hearing out obnoxious' is 'YAHOO'.
(Other definitions for yahoo that I've seen before include "Brutal lout" , "Coarse or brutish person" , "Brute; hurrah" , "Uncivilised brute(Swift)" , "Swift chap" .)