Considering the rule is only self-imposed, it's pretty self-selective.

"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."

In essence, it's a rule about how you allow people communicate to you, rather than how you communicate with others.