Well there is no such point that coffee could make a drunken person calm. Because coffee we know that it contains caffeine, which is used widely as form of stimulants worldwide. It enhances mental focus.
In some studies coffee may counteract the sleepiness in which a person brought about by the consumption of alcohol. Coffee could not totally eliminate the alcohol from a drunken person, but coffee increase the speed of the liver to detoxify the alcohol, but if you give some coffee to someone who is drunk, what you will get is not a calm person but a wide-awake drunk from caffeine effects.