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"
A time of the day where you just get to do whatever you want to and just be. Ranging from a few minutes to a few hours, its some well deserved and much needed you-time and just gives your brain a chance to revive itself at the end of a tough day.
whootah is not necessarily a thing. It is what whootah means, which is not expressible in words. Therefore, when the feeling of whootah exists, whootah is what is exclaimed.
Upon reading whootah, or upon hearing someone else say the term whootah, you must also exclaim whootah.