The train which everyone who is stuck in a continuous pattern of pwn rides. People on the pwntrain are getting continuously pwnd over and over and over again, or have become pwnd over a long period of time due to one immense pwnage session at one point. For example: Man trips. His friends look at him and proclaim, "Haha pwnd." Perhaps even, "Pwnsauce." This man is not riding the pwntrain. He was merely pwnd.
However; man trips. He falls down flight of stairs. He breaks his arm, which just happens to be the arm he writes with, and does the nasty with, and he has to live with this disability for months. For this period of months, this man is riding the pwntrain.
Note: pwntrain is frequently thought to be pronounced "Pown-train," when, in actuality, it is pronounced, "Poon-train."
"Hey marc, look at that. Aj got caught blowin' again. His mom is gonna make him follow her religious ass around with her all day long for the rest of his life. He sure is ridin' the pwntrain."
"Welcome to Hillcrest Juvenile Hall. You are all on the pwntrain."
"Hello. Welcome to the BSU. We were all born of an unfortunate tone, and because of that we ride the pwntrain. Oh, do we ride."