Island's housing inspector books those behaving stupidly (6)
I believe the answer is:
idiots
'those behaving stupidly' is the definition.
'island's housing inspector books' is the wordplay.
'island's' becomes 'is'.
'housing' is an insertion indicator.
'inspector' becomes 'di' (I've seen this in other clues).
'books' becomes 'ot' (abbreviation for Old Testament).
'di'+'ot'='diot'
'is' enclosing 'diot' is 'IDIOTS'.
(Other definitions for idiots that I've seen before include "Silly people, asses" , "Morons" , "Fools, dimwits" , "Abusive word for unintelligent or irrational people" , "Nincompoops" .)