The Infamous OPP
OPP was initially coined to reference the situation where in a polyamorous cis het couple relationship, the cis man sets a rule where there could only be one p-nis. All partners dealing with him are expected not to engage intimately with other cis men unless otherwise stated. The one p-ni policy shows up not just in polyamory but also in the sw-nger community, open relationships, and arguably platonic friendships. One p-nis policy in its original form - term and practice - is transphobic (among other things). For a more inclusive application, Depending on the parties involved, it can be used instead to reference one private (part) policy or one p-ssy policy. For these slides, opp is referencing the misogynistic, transphobic, heteronormative, and bisexual f-tishization form of the term where a cis het man sets a rule for the women he is dating. To be clear - trans and cis women can be the victims of an OPP dynamic with a cis het man.
OPP's focal point is p-nis and the binary. "if one is a man, they must have a p-nis." The "policy" wrongly assumes all people with p-nises are men, under the premise that having a p-nis must mean you are a man. For the trans men who may not have a p-nis, opp automatically excludes and misgenders them.
How It's Sold?
A lot of the time, when a woman brings up that she can not date other men - she is unaware of the fact that this is misogynistic behavior. Typically this is more successful with polyamorous women who have internalized misogyny. It is not difficult to sell the lie of how more than one p-nis devalues a woman's worth to other men then. Sometimes these cis men may talk about being an "alpha" and how another p-nis's presence would somehow correlate to their ability to protect their partner. They may also weaponize religious texts. Oftentimes these reasonings are given with spoken and unspoken ultimatums. The threat of ending a relationship, violence, or devaluation of their partner usually follows close behind.
How's It's Maintained?
With the looming threat of losing a relationship, being devalued, or possible violence for even bringing up the topic of wanting to pursue intimacy with someone with a p-nis, many women don't even challenge it. Some women do not know they are in an opp relationship until they try to pursue someone that fits into that policy's restrictions. Western society also condemns women for being with multiple p-nises. The couple/unit may find themselves only seeking intimacy with (or outside of) each other with people who appear to be cis women. Even if the partner of the cis het man only had no interest in other cis men, opp is still there underneath it all, just in case.
"It's My Choice!"
"It's my choice to be opp! I didn't want to date other men anyways." Beyond the fact that statement is inherently transphobic - you do not need to make a choice, a policy. The women coupled to a cis het man who only seeks queer relationships for themselves do not need to announce OPP, or they can't date "other men." Your choice did not need a rule with consequences attached from your partner.
Despite how you feel about someone's opp relationship - tread lightly. Even if you suggest that the woman reaccess the rule and why it exists - keep in mind that some would be at risk of abuse for even suggesting an amendment to the policy. You do not have to date someone "under" this policy; even if it does not affect you presently, it could. Some cis men extend their policy to their new partners and metamours.