Origin: Acronym, Army lingo.
I often heard this acronym during my stint in the army. NATO is used to describe a person who does not walk his talk.
NATO in this case is used as an acronym : “No Action, Talk Only”
“That bugger every time says he is best in this and best in that, when it comes to doing the actual thing he either act blur or push someone else to do it. He really is NATO.”