“Your Fly Is Open” – Meaning & Facts (British vs. American)

The phrase “your fly is open” is generally a humorous way to remind someone that they’ve forgotten to do something after a toilet break. Of course, there is more than one way to say it, and it differs from British and American English, and this article will explore that.

What Does “Your Fly Is Open” Mean?

“Your fly is open” means that someone has forgotten to zip up their trousers after going to the toilet. It mostly applies to men when they unzip their trousers to use urinals, though it is possible that a woman may forget to zip up her trousers in a similar fashion.

What Does "Your Fly Is Open" Mean?

We use the phrase in a jesting tone. It often means that we want to indicate that they’ve forgotten to zip up while trying to keep it civil and funny so that they’re not too embarrassed about it.

It can be a fairly embarrassing occurrence for many people, which is why it’s wise not to draw too much attention to it. Typically, you won’t want to announce the phrase “your fly is open” to a room full of people, and you’ll often want to take them aside and have a bit more tact about it.

What Is The Origin Of “Your Fly Is Open”?

While we now know the meaning of the phrase, it might help us to explore the origin a little more. It’s an old-fashioned phrase, but one that seems to have stuck around, even when the original “fly” is rarely in existence today.

The phrase originated when “fly buttons” were used on trousers in place of zips. It refers to the seam where you can unbutton it to help relieve yourself in a toilet. People would say “your fly is open” when referring to the seam not being buttoned up.

Generally, we use “fly” in the singular form to talk about it since it’s only one seam that we’re referring to.

We say “your fly is open” when someone hasn’t zipped up their trousers today since buttons aren’t nearly as common as they used to be.

Interestingly, buttons were more common in Great Britain than in America, which led to some interesting language differences.

Is It “Your Fly Is Open” Or “Your Flies Are Undone”?

There are two possible ways to use the phrase. Most of the usage depends on which language you’re speaking with, and it relates to the origin of the phrase and how fashion trends differed in both Great Britain and America.

Both “your fly is open” and “your flies are undone” are correct. They both appear in common English, and you might hear them in both US and UK English.

To help clarify the differences between the two phases, it might help you to see some visual statistics. We’ve put together some graphs for you so that you can understand the differences.

According to this Google Ngram Viewer graph, both phrases are common and correct. However, it’s clear that “your fly is open” is more popular, and that’s because it’s the US English variation, which has a much greater impact on the language choices of the world.

your fly is open vs your flies are undone

We can narrow the information down further with this American English graph from Google Ngram Viewer. In American English, “your fly is open” is the only correct phase, and there is no mention of “your flies are undone.”

your fly is open vs your flies are undone American English

In contrast, this British English graph from Google Ngram Viewer shows that “your flies are undone” is more popular, but “your fly is open” is still a common saying, especially since American English is growing in usage and slowly taking over British English phrases.

your fly is open vs your flies are undone British English

The key difference between the two languages is because of how the different countries viewed the origin. In American English, the word “fly” refers to the seam where the buttons and zips are sewn in, which is why they use “fly” as a singular word.

However, in British English, “flies” is plural because it refers to the number of buttons on the trousers that are undone. For this reason, they always stuck to the plural form of the phrase and never thought about changing it until recently.

If I Am Not From The UK Or The US, Should I Use “Your Fly Is Open” Or “Your Flies Are Undone”?

While it’s great to know what the UK and the US do with this phrase, that isn’t much help if you’re from another country. It’s even harder to know which phrase you should use if you’re from a non-English-speaking country entirely.

If you’re not from the UK or the US, you can use either phrase, but “your fly is open” is generally more common.

However, there are plenty of cases of overlap, which is why we don’t need to give you an exact answer. You can say “your flies are undone” in American English and “your fly is open” in British English, and most, if not all, native speakers will know what you mean.

In American English, it’s also common to shorten “fly is” to “fly’s,” making the saying “your fly’s down.” In this case, there’s hardly any phonetical distinctive between “fly’s” and “flies,” which is why it’s so common for both countries to use either phrase.

Is It “Your Fly Is Open” Or “Your Fly Is Down”?

Within the phrase itself, you might come across the adjective “open” or “down.” Again, the key differences come from whichever language you’re using, and we’ll look into them more now.

“Your fly is open” is the correct form, though both are used. It’s more common for most native speakers to use “your fly is open” when they want to talk to somebody who forgot to zip or button up their trousers.

To emphasize the differences, we can look at the following Google Ngram Viewer graph. This shows common English usage across both American and British English. It’s clear that “your fly is open” is the most popular choice, but “down” still gets used.

your fly is open vs your fly is down

This Google Ngram Viewer graph shows us what American English looks like. Here, it’s common to use “your fly is open,” and “your fly is down” is much less popular. However, both phrases are still used.

your fly is open vs your fly is down American English

Interestingly, you’ll see a key difference with British English from Google Ngram Viewer. Only “your fly is open” is correct in British English, and there are no recorded uses of “your fly is down.”

your fly is open vs your fly is down British English

Examples Of How To Use “Your Fly Is Open” In A Sentence

We’ve covered as much as we need to about the general usage, so it’s time to look through some examples. With these, you’ll have a much easier time understanding what the phrase means and how you can use it.

  1. I’m sorry, but your fly is open! Can you correct that before we continue this conversation?
  2. Is my fly open? Oh my word, I’m so sorry!
  3. I hate to be that guy, but your fly is down, and it’s really offputting!
  4. Your flies are undone, and it would be much more professional if you could do them back up again.
  5. Hey mate, don’t look now, but your fly’s open!
  6. His flies are undone, which makes him look really silly next to all of those professionals wearing suits!
  7. I can’t believe your fly is still open! You’ve got to correct that before someone else notices!
  8. My fly is open, and I’ve only just realized! I hope nobody else noticed.
  9. I’m so sorry, but your fly is down! Would you be kind enough to do it back up before the boss gets here?

We can use the phrase when we want to tell somebody that they’ve forgotten to zip up after a visit to the toilet. It’s usually something that’s quite obvious to look at, which is why it’s appropriate to tell people about it before everyone notices.

Should You Tell Someone Their Fly Is Open?

The phrase itself comes with some questions about etiquette. Most of the time, people will think it’s quite rude if you try and use the phrase.

You should only tell somebody you know that their fly is open unless you’re in a professional environment. If you are in a formal setting and notice that someone’s fly is open, you might want to take them to one side to correct it quickly.

The reason it’s important with formal situations is because of how bad it looks. It takes away from the sincerity of people if they’ve left their fly open, so if you can highlight this to them in a positive way, it’ll save them from a lot of grief and embarrassment.

However, in informal situations, you don’t have to worry about being as secretive. Instead, you can make a joke about it with your friends.

How Do You Politely Tell Someone Their Fly Is Open?

Finally, let’s look at some polite synonyms for telling someone their fly is open since it’s not the best way to talk to somebody. All of these variations work really well in its place.

  • I’m sorry, but you’ve forgotten to zip up.
  • Your zipper is down