Awfully vain, the German attacker (7)
I believe the answer is:
invader
'attacker' is the definition.
(I've seen this before)
'awfully vain the german' is the wordplay.
'awfully' indicates anagramming the letters.
'the german' becomes 'der' ('the' in German).
'vain' with letters rearranged gives 'inva'.
'inva'+'der'='INVADER'
(Other definitions for invader that I've seen before include "One entering as an enemy" , "Trespasser" , "far from welcome guest" , "Attacker from abroad" , "One attacks" .)