More often than not, as far as train wrecks go, the ass end of a train wreck is arguably the most desirable position one might occupy whilst finding they are in the midst of a train wreck in process. The exception to this principle, of course, would be in the event that a train got ass wrecked. Even so, the ass-end of the offending party would most certainly fare significantly better than that of the violated party.
Boy: "Hey, Girl, did you have a rough night last night? You look like you just crawled out of the Ass End of a Train Wreck."
Girl: "Maybe so, but if you think I LOOK bad, I FEEL like that Train must have gotten Ass-Wrecked."
It is when a girl flexes her asshole open and a guy blows weed smoke into her asshole. And clenches her asshole tight. While peeing in her vagina then fucking her until she orgasms then having the man's pee and the weed smoke blast out as she orgasms.