Crocker's rules, named after and framed by Lee Daniel Crocker, is a social communication protocol or etiquette used to reduce emotional impact on debate. Crocker was an early contributor to Wikipedia, and, with Larry Sanger, Fred Bauder and others who chose to contribute pseudonymously or anonymously, helped to form its rules to maximize objective reporting.
By declaring commitment to Crocker's rules, one authorizes other debaters to optimize their messages for information, even when this entails that emotional feelings will be disregarded. This means that you have accepted full responsibility for the operation of your own mind, so that if you're offended, it's your own fault. The underlying assumption is that rudeness is sometimes necessary for effective conveyance of information, if only to signal a lack of patience or tolerance: after all, knowing whether the speaker is becoming angry or despondent is useful rational evidence. Two people using Crocker's Rules should be able to communicate all relevant information in the minimum amount of time, without paraphrasing or social formatting.
Thus, one who has committed to these rules largely gives up the right to complain about emotional provocation, "flaming", "trolling", "abuse" (hopelessly subjective terms) and other alleged violations of etiquette. They give these rights up in the interest of effective debate.
Note that Crocker's Rules does not mean one is authorized to insult people; it means that other people don't have to worry about whether they are insulting you. Crocker's Rules are a discipline, not a privilege. Furthermore, taking advantage of Crocker's Rules does not imply reciprocity. How could it? Crocker's Rules are something you do for yourself, to maximize information received - not something you grit your teeth over and do as a favor.
In contrast to radical honesty, Crocker's rules encourage being tactful with anyone who hasn't specifically accepted them. This follows the general principle of being "liberal in what you accept and conservative in what you send".
Crocker emphasized, repeatedly, in Wikipedia discourse and elsewhere, that one could only adopt Crocker's rules to apply to oneself, and could not impose them on a debate or forum with participants who had not opted-in explicitly to these rules, nor use them to exclude any participant.
A lack of freedom to make emotionally uncomfortable observations is often thought to lead to groupthink. The assertion that unanimity is not consensus arises from common anecdotal evidence that disagreement is often not expressed not because it is not relevant, but not pleasant, and that poor decisions are often unchallenged as a result. This principle is ancient, and dates back at least to the ancient Hebrew Sanhedrin wherein unanimous decisions were considered unfair by nature and represented only the lack of adequate defense of the accused. A voluntary adoption of Crocker's rules would presumably eliminate at least some cases of disagreeable silence and make more objections explicit, as in the practice of appeals and supreme courts, where the minority opinion is codified with the same care as is taken with the majority's.