To "earn", is crimnal talk for making money. Mostly career criminals use this term such as italian, irish, or jewish gangsters. They have to "earn" somehow. They find all sorts of ways to earn.
Nicky Santoro on Casino:
"What the fuck they expect from me, I had to earn didnt I?"
To get ratted during a poker game. May lead to you quitting cards if you're a little bitch.
The term came about as a sarcastic comment to say after you either got ratted or rivered during a hand.
That was a great earn.