While having sexual intercourse with a women from behind, doggy style. You hold onto her hair, with every thrust you yell "Chugga, Chugga, CHOO-CHOO" and slide forward in a complete circle.
Guy 1: So how was it last night?
Guy 2: Amazing! I ran the D Train on her all night, wore out a path on the carpet.
Girl 1: what did you do last night?
Girl 2: Took a ride on the D Train, best ride of my life.