They believe content is enough and communication is a luxury. So they keep you out of the loop (until it's too late) or they embarrass you in meetings.
They speak Data, not English. They prize research and rigour so highly that they can't craft a good call to action, couch an idea in a seductive way, or cut to the chase.
They present with little confidence. What they do present is shrouded in so much background you don't have time to listen to all of it.