Second, lack of politeness is a countersignalling method to indicate friendship and community by showing you are close enough to a person that politeness is unnecessary

As you say, that only works if everyone is already on board with this. What the OP is talking about is, effectively, the situation where you're saying "hey nigga wassup!" to someone you've just met or barely know. In order to use direct communication to signal closeness, you need to be sure that you're on the same page first.