The term 'bool train' refers to somebody beginning to use drugs or drink for the night. The train can't be stopped and its tracks derail your day. It can be used to describe an event and an action.
The word bool is a refrence to the song "Bicken Back Being Bool" by YG. He uses bool to describe a drugged out hazy state, throwing back with his pals "just bicken back being bool."
"let the bool train begin folks."
"my day has been so bad im just gonna go home and hop on the bool train"
"he got hit by the bool train"
"ive been on the bool train way too much lately"