It would have been most undiplomatic to prove it.

His Venezuela dispatch, however, was one of the most undiplomatic documents ever issued by the Department of State.

They did the most undiplomatic thing that can be done; they concealed a breach of partnership without even concealing the concealment.

You could say he was the most undiplomatic diplomat Washington ever had here, said Ruediger Lentz, executive director the Aspen Institute Germany.

In the protocol-ridden world of the UN, to promote oneself as a contender to be the world's top diplomat is considered most undiplomatic.