Green’s Dictionary of Slang

1. (US) of an individual, one who is wholly emotionally unstable.

2017		J.R. Lawrence My Camp 7: I stood outside the shop thinking to myself, this guy is a fucking train wreck.
2020		S.A. Crosby Blacktop Wasteland 123: Ronnie was going to try and fuck him over for his cut. Quan was a fucking train wreck.

2. (US) in sporting terms, a collapse.

2008		D. Jenkins Franchise Babe 144: It [i.e. a ‘whiffed’ golf shot] was an embarrassing example of an athlete having a train wreck.
2012		R.A. Dickey Wherever I Wind Up 323: I could easily have let these things turn my season into a train wreck, but I managed them well.

3. (US) as sense 2 but in non-sporting contexts.

2018

W. Kramer Hard Stuff 93: We [i.e. a rock band] could be absolutely brilliant one night, and a train wreck the next.