Percy: This sounds like a terrible idea, but ok.
Typically, one pours the contents of the instant coffee packet directly into the mouth, followed quickly by a swig of water to dissolve the grounds and wash it down. If feeling particularly creative, one may add the included sugar packet to the instant coffee packet prior to taking the shot.
This allows the caffeine contents of a medium sized cup of coffee to be swallowed in a matter of seconds. This is usually a last resort for soldiers who must remain awake, because the high comes quickly and is often followed by a severe loss of energy.