Bad manners to reveal decorations (9)
I believe the answer is:
ornaments
'decorations' is the definition.
(I know this)
'bad manners to' is the wordplay.
'bad' is an anagram indicator.
'manners'+'to'='mannersto'
'mannersto' with letters rearranged gives 'ORNAMENTS'.
'reveal' is the link.
(Other definitions for ornaments that I've seen before include "Decorations, embellishments" , "Decorates" , "Tree embellishments" , "Trinkets" , "Adornments, decorations" .)