First, what IS the One Penis Policy?

The OPP is a set of boundaries, that describe a relationship defined by the following rules:

One male (usually cissexual and hetero) is (or wants to be) in relationships with multiple cis women. The relationships also usually are not closed.
The female partners can date other women (or each other), but not any other person having a penis (which almost always includes trans women).

There may be some other rules and attributes that usually come along, but only those mentioned are defining the OPP.

Did you understand the definition? Let’s have a quick test and decide which of those scenarios are One Penis Policies:

A man has a wife and a girlfriend. The women are in no relationship with each other. Even though they’d like to, they don’t date other man because it would really upset the first one.

Yes, this is obviously a OPP, fulfilling both rules.

A mutually agreed closed Throuple consisting of two women and one man.

No. The OPP is about regulating in which way the relationship is open, while this relationship construct is obviously closed. People who attack the OPP also don’t mean to attack Throuples or Triads in general.

A couple of Unicorn Hunters™ (a man and a woman) looking for a woman to date together

Too little information. While people see problems with the principles of unicorn hunting, it doesn’t always imply a OPP. You can argue about probabilities here, but judging people based on stereotypes is still a big no-no.

“But you still haven’t told us what the problem is when everyone is adult and consenting!”

Yes, consent is important, but that’s not the actual problem. First of all, if you are fine with your women having sex with other women but only if there is no penis involved is a perfect example of not perceiving men and women as equals. This defining rule of the OPP is inherently sexist. So, if you have a problem with sexism, this is one of its symptoms. (Also, this often goes along with fetishizing lesbians.)
Furthermore, if the women are only allowed to date cis women you can add transphobia to the list of offenses.

Frequently Asked Questions

Is *insert a relationship scenario* a OPP?

There are two rules to check, it’s not that hard.

But what if it’s not that obvious?

Then hold your horses and don’t assume anything. That’s just basic human decency.

What if I see an obvious OPP?

I don’t know, what do you do when you see sexism? Your actions may vary depending on your anger towards society.

What if I don’t have a problem with sexism and such?

Then you don’t have a reason to dislike the OPP or even be on my page. Go away.

Is there a One Vagina Policy?

Yes. Anecdotal evidence suggests that it’s far less common, but it works basically the same way: A women* does not want their male partners to have sex with other women* while they have other male partners and maybe fetishize gay men*.

Where are non-binary in all of this?

This terminology was started with cis male people in mind the describe a seemingly common occurrence, focusing on the genitals because trans women were treated as men* in this scenario and trans men as women*. You can try to apply the terms OPP and OVP to scenarios centered on non-binary or trans people, but without a common narrative people it could be difficult for people to understand what you mean. But for what I care just try and explain what you mean.

My philosophy is live and let live.

That’s not a question, but I’m not surprised since you don’t seem to be grasping what you read, anyway.

Are you actually a rat?

I like this narrative way more than the conspiracy theory that I’m a stack of cats in a trench coat.

How do you know all that?

I use terminology. This is the thing where you look up what words mean and use them like they’re meant to be used.