I saw the movie, there is no mention of train or something that is close related to the title.
Plot:Lead Actress make love to everyone she likes, but her relations screwed up.
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The literal meaning of
Train wreck : Someone who is in a terrible situation, someone who is a disaster.
Accordingly the Title is perfect for the movie as in the movie we see Amy is a true jerk. She’s selfish. She’s rude.and these all nature always led her to terrible situations and which gives her persona of being a disaster.