A Coal Mine is an insult from a friend or family member that uses an embarassing or deepsecret of your's to hurt or embarass you. Usually used in a large crowd (where it has more exposure to others.) or to use against you.
1. Bill doesn't have a girlfriend anymore because his brother Coal Mined him in front of her.
2. "Hey Bob, get me a drink."
"Why should I?"
"Hmm... Perhaps you've told me something I can Coal Mine you with."
The thankless task of being the first one to take a hit, from the practice of coal miners of bringing down a caged canary to see if there's dangerous gas below
I don't know if this alleyway's safe, and I ain't no canary in a coal mine.
When a kid from northern PA takes a shit on an ice cube tray freezes the shit then puts the cubes in a friend's asshole whilst trying to light the cubes like coal
Dominic got tired of Duncan's crap so he gave him a shamokin coal mine