Lacking diplomacy (8)
I believe the answer is:
tactless
'lacking diplomacy' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for tactless that I've seen before include "Without subtlety or sensitivity" , "Indiscreet" , "Lacking sensitivity, saying the wrong things" , "Lacking diplomacy" , "Unlikely to make Diplomatic Service" .)