In the game of Risk, this refers to the semi-rare, usually late-game event of one player dropping like a hundred fucking armies somewhere in Asia, then rampaging from one end of the board to the other. Typically one or more players will be eliminated during this process, and several more will call the rape-train operator a "douche" or a "little bitch."
Player A: Holy balls, you just went from Western Australia through Kamchatka, all the way across North and South America, up through Africa to the Ukraine!
Operator: All aboard the rape train! Wooo wooooooooooo!
Player B: Douche.