A trainwreck is something — or someone — that has gone wrong so completely that it is almost impressive. The literal meaning is a train crash, and the figure of speech keeps the whole scene: something large, moving fast, that cannot be stopped, and that people cannot stop staring at either. So a job interview that goes badly from the first question is a trainwreck; a company launch where nothing works is a trainwreck; a film with a confused story and bad acting is a trainwreck. Used of a person, it means someone whose life is visibly falling apart — money, relationships, health all going wrong at once. That use is harsh and can be cruel, so be careful: it is fine about yourself ("I was a complete trainwreck that year") and fine about a public figure in a joking way, but said about a friend or a colleague it is an insult. There is also a common phrase, watching a trainwreck in slow motion, for seeing a disaster coming and being unable to look away or to stop it. The word is informal and modern, at home in conversation, social media, and reviews, and out of place in a business report or an essay. You will see it written three ways — trainwreck, train wreck, train-wreck — with the two-word form more usual in American writing; all are accepted.