greater than ninety

By the rules of tenuous analogy, the correct way of dealing with obtuse people would be to argue them right into a tight corner, preferably one tighter than a right angle. Alternatively, acting reflexively could defeat them at their own game. It's often unclear whether or not someone is acting that way disingenuously rather than out of an inability to think logically, or at least logically according to the normal rules of logic which usually operate in this particular reality. One of the most noticeable absences caused by the lack of machines which can decode thoughts is a sort of process-logging helmet which would emit a constant stream of printed tape from the rear showing the working of the wearer's current thinking, which would make it clear from which direction any visible obtuseness had been approached.