When a group (minimum of 5) of Asian men or combination of men and women (wearing strap ons) form a straight line (front-to-back) resembling a train and then engage in vaginal or anal sex with the person in front of them.
Tom: Hey where's Megan at? I thought she was joining us for dinner?
Louis: No, Asian Mike invited her over to his place tonight. She's going to be the "locomotive" in their Orient Express sex train tonight.
Tom: Well that makes sense...she's got a great caboose!!!