Bursting into a prolonged fit of intense, uncontrollable laughter. Used to describe how you feel inside when you find yourself in a pleasing set of circumstances, or at least in comparison to a worse outcome that also might have occurred. Instigating this sort of reaction in someone is called making that person "crack laugh up".
Mikey told me a hilarious joke the other day with his crazy accent, and I couldn't stop crack laughing!!!