A blanket-term that can be used in almost any situation, usually said in such a way that the other person still understands what you mean.
Origin: On the Xbox 360 store page, most games had lengthy descriptions that summarized the game in order to encourage you to buy it. The video game 'Gun' however simply had the words Ambush The Train in the description and nothing else.
Example 1-
Jane: "Hey dude, how's it going?"
Joe: "Ambush the train..."
Jane: "That bad, huh?"
Example 2-
*Very attractive person walks by*
Internalized: 'Ambush. The. Train.'
Example 3-
*You jam your toes in the garage door*
You: "AMBUSH THE TRAAAIN!!"