A phrase used to indicate that the target is about to be introduced to a whole world of pain. Specifically, you, by opening this can, are going to unleash the power of whooping (that is, in the sense of attacking and beating, not in the sense of whooping cough) upon their sorry ass.
1. Specific use:
Jerry paused in thought.
"For what you have said about my mother, my girlfriend, and the proud ancestry of my forebears," he announced, "I have every intention of opening a can of whoopass."
2. General form:
"If <offending body> continues with <offending action>, it is totally time to open a can of whoopass"
1. Used by parents to discipline insolent children, performed by hitting the child's buttocks or other areas of the body forcefully several times. Usually performed with a hand or other object such as a belt, spatula, or nine-iron golf club.
2. General saying for a physical assault, with the prospect of the assaulter ending the altercation favorably.