The best way to rant is to not rant and instead figure out how to transform your critique into a constructive, useful question.
For instance, Windows 8 is currently a controversial topic in the UX community. You could post a rant about this, which I'm sure could be very thoughtful and compelling, but would be off-topic for our site. Or you could transform it into a question. But you would have to extract a useful question that other people would have and that is answerable by the UX community.
A bad question to extract: Is Microsoft making the right choice by deciding on such a radical change from the Aero interface? This question isn't answerable because no one can know something that hasn't happened yet. It would be closed as subjective and inflammatory.
An example of a better question: What research has Microsoft done that influenced its decision to move forward with Metro on the desktop? This question is direct, answerable and actually quite interesting. The only problem is that the research you ask for may not actually be available - but you can't really know that until you ask and someone pulls it out of a hat or someone from Microsoft stops by.
If the topic is controversial enough that you feel the need to rant about it, I'm sure there are lots hidden questions you can uncover. Asking them here would certainly gain you a lot of reputation. And you could even try answering them yourself (as long as your answer is useful and not a rant!).
Rants are often your answers to unasked questions. Try asking the questions and see what you can learn from our community.