So rudely misbehaving, creating the wrong impression (8)
I believe the answer is:
delusory
'creating the wrong impression' is the definition.
(delusory means misleading or deceptive)
'so rudely misbehaving' is the wordplay.
'misbehaving' indicates anagramming the letters.
'so'+'rudely'='sorudely'
'sorudely' with letters rearranged gives 'DELUSORY'.
(Other definitions for delusory that I've seen before include "Deceptive" , "Misleading - rudely so (anag)" .)