Crocker's rules, named after and framed by Lee Daniel Crocker, is a social communication protocol or etiquette 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. 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.
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.
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.