When someone has no self respect or standards and solely hooks up with a string of women he does not know or care to know. Generally a douche bag.
Friend 1, "Man, Jeff sure has been hooking up with a lot of random woman"
Friend 2, "yea, he has really been riding the strange train lately"
"Fucking guy has been on the strange train for a solid month now.
"Wow, he really jumped back on the strange train after his break-up"