A Modest Boast is joking about how good, something about you or something owned by you is. Unlike real boasting a Modest Boast is used as a joke or comedy form to make people laugh.
1. "Haha! He is so funny."
"What's so funny about him bragging and boasting about his self?"
"Calm down dude, its just a Modest Boast."
A Coal Mine is an insult from a friend or family member that uses an embarassing or deep secret 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."