Every social context has norms that aren't written anywhere but are understood by participants. CNM has developed its own set of these, some that make sense when you understand the reasoning, others that are community-specific and not universally held. Knowing them before you violate them is useful.
Disclosing your relationship status clearly and early
In CNM contexts, disclosing that you're non-monogamous, and in what configuration, before romantic interest is expressed or pursued is considered basic courtesy. The principle: people deserve to know what they're being invited into before they're invested.
"I should mention I'm in an open relationship" said on a second date is considered late; mentioning it in a profile or in initial conversation is standard. The degree of detail expected at each stage varies, but the expectation of disclosure itself is strong.
Not outing partners without permission
CNM involves multiple people with varying levels of outness in different contexts. Not all of your partners will be out about non-monogamy to all of their contacts. Disclosing the existence or details of someone else's relationships, including to your other partners or mutual connections, without explicit agreement is a significant breach of trust.
The implication: when you're new to a polycule, don't assume that information flows freely between everyone. Ask what's shared with whom. Particularly in contexts where people have professional or family reasons to keep their CNM private, the default should be discretion.
Sexual health communication
Transparent communication about sexual health testing, results, and practices is a baseline expectation in CNM. This includes disclosing new sexual connections to relevant partners (as agreed), not making barrier decisions unilaterally when agreements exist around them, and getting tested at agreed intervals.
"Fluid bonding" (barrier-free sex between specific partners) involves explicit conversations, not assumptions. The assumption that an existing relationship includes barrier-free sex when nothing has been explicitly agreed is a common and significant mistake.
Event and community space norms
CNM social events, whether munches, discussion groups, or parties, have developed their own etiquette:
At vanilla (non-explicit) meetups, explicit sexual discussion or behaviour isn't expected or appropriate. These are community spaces for people to connect, not play spaces.
Don't assume that attendance at a CNM event signals interest in you. Polyamorous people at a polyamory event are there for community, not necessarily available for approach.
Couples attending CNM events as a unit who are clearly hunting together, approaching single people as a package, is generally received poorly in CNM communities that have experience with unicorn hunting dynamics. This is less a moral rule than a practical observation about how it lands.
Not over-processing in public
CNM communities value communication, but there's a distinction between healthy communication and processing your relationship dynamics in community spaces in ways that put others in the middle. Asking metamours to mediate conflicts, venting about partners in shared spaces, or involving the community in individual relationship dynamics is generally considered a breach of appropriate use of community.
Respecting relationship structures you don't share
CNM encompasses a wide range of structures, from hierarchical to non-hierarchical, from swinging to relationship anarchy. The etiquette of CNM community spaces, at least the healthier ones, includes not treating other people's valid structures as suspect or lesser.
In practice this means: not treating hierarchical polyamory as inherently problematic, not treating swinging as less ethical than romantic non-monogamy, not treating solo polyamory as commitment avoidance. These communities have enough friction with mainstream society without turning their diversity into internal hierarchy.
Gatekeeping who counts as CNM
Debates about whether someone is "really" polyamorous, or whether their practice is "ethical" enough to count as CNM, are a feature of online and sometimes in-person CNM communities. These debates are mostly unhelpful. The etiquette principle: let people define their own relationships and focus on whether your own practice meets your own standards.