The trick is trying to understand/figure out if the person you are dealing with is your enemy or if the org he is dealing with is the enemy. If it's the latter then you want to recruit mutual empathy so he becomes your advocate in his org. That's the situation where being angry is counterproductive because it makes it easier for him not to care about your problem. Conversely, if you believe the person you are dealing with is the immediate problem, then a threat (if it's a legitimate one you can back up) becomes more useful/needful.