Don't be a ****. If people abided by this, we wouldn't need any other policies about behavior. This is a corollary of ignore all rules, and most other rules are special cases of this one.
Fundamentals
"Don't be a ****" is the fundamental rule of all total social spaces. Every other policy for getting along is a special case of it. Although nobody on WP is empowered to ban or block somebody for being a **** (as this would be an instance of being a ****), it is still a bad idea to be one. So don't do it.
No definition of being a **** has been provided. This is deliberate. If a significant number of reasonable people suggest, whether bluntly or politely, that you are being a ****, the odds are good that you are not entirely in the right.
Being right about an issue does not mean you're not being a ****! ****s can be right — but they're still ****s; if there's something in what they say that is worth hearing, it goes unheard, because no one likes listening to ****s. It doesn't matter how right they are.
Being a **** isn't equivalent to being uncivil or impolite (though uncivil and impolite ****s are not unheard of.) One can be perfectly civil and follow every rule of etiquette and still be a ****. The use of a vulgar term to convey the concept is intentional and serves to distinguish this principle from issues of politeness and other protocols of interaction. To avoid being a **** is not a matter of obeying etiquette but is a broader and more important concern.
Coping with being labeled a ****
If you've been labeled as a ****, especially if you have been told this by several people in a particular community, it might be wise to consider the possibility that it is true. If you suspect that you may be a ****, the first step is to become aware of it. Ask yourself what behavior might be causing this perception, and if you can't work it out, politely ask those that perceive it to explain or clarify. Once you have determined which behaviors are causing the problem, try changing them and your mode of presentation. In particular, identify the harsh words in your communications and replace them with softer ones.
Honestly examine your motivations. Are you here to contribute and make the project good? Or is your goal really to find fault, get your views across, or be the one in control? Perhaps secretly inside you even enjoy the thrill of a little confrontation. This may not make you a bad person, but to everyone who is busily trying to build something great, you become an impediment. People get frustrated, rancor ensues, the atmosphere changes, and the whole project suffers. Are you here to give, or to take?
If appropriate, publicly apologize to anyone to whom you may have been a ****. It's okay; this won't make you seem weak. On the contrary, people will take notice of your willingness to cooperate and will almost always meet your efforts with increased respect.