Rants are undefinable, as it's doubtful you actually need to have more than one sentence in order for something to qualify as a rant; to be frank, I'm sure of it, and I don't think we need to be going around and pointing our fingers, hem-hawing at those who happen to like a good rant now and again or those who don't like them, especially when we can't seem to agree on what it takes for something to be a rant or even the concept that a rant is somehow quantifiable by the number of sentences, though perhaps character counts could shed some light on it if you're looking for more accuracy, which I doubt that you are.