Decoration to annoy (6)
I believe the answer is:
ruffle
I believe this is a double definition.
'decoration' is the first definition.
(ruffle is a kind of decoration)
'to annoy' is the second definition.
(ruffling is a kind of annoying)
(Other definitions for ruffle that I've seen before include "Disrupt smooth surface" , "Agitate" , "Ornamental frill; make disarranged" , "Aggravate" , "Upset the composure of" .)