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1.
A method used by soldiers to quickly ingest the instant coffee found in MREs.

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.
Platoon SGT: Those of you on fire watch MUST remain alert tonigt, take ranger shots if you have to, but we move out at 0400.
by JoePilot April 27, 2007
 
2.
A drink made from extremely cheap, yet potent vodka (e.g. Taaka). A shot glass is turned upside-down, and a small amount of vodka is poured onto the bottom of the glass, filling the tiny depression. The person taking the shot then snorts the vodka, once into each nostril.
Wilks: Hey Percy, you should do a Ranger shot!

Percy: This sounds like a terrible idea, but ok.
(Sniff)
Percy: HOOAH!
by jMikey93 April 29, 2012