1. During the act of doggy-style vaginal intercourse, the male, while recovering from a thrust, pulls out too far and his penis "accidentally" inserts itself into the girls anus.
2. An arctic map in the video game "Call Of Duty: Modern Warfare 2."
"The other night my girl moaned some other guys name, so I derailed her. See if she does that again..."
"Last night I was having some fun, then got derailed"
"You pulled out too far and got mud on your junk?"
"Worse. I got that shitty snow map."