Open fly

An open fly refers to the usually unintentional leaving of the fly of one's trousers unzipped, unbuttoned, or otherwise open. Often the underwear underneath is visible.

It is often considered humorous to many if a person is caught with his or her fly down. The idea of the fly being down has been used as a humor device in films, and, as internet blogs continue to gain popularity, many blogs have spent time pointing out that notable people (e.g. President George W. Bush [1]) have their flies down. The analogous phenomenon with cars, referring to the gas cap, can use some of the same phrases and be shown in blogs as well (e.g. David Carradine ).

In the 1980s, Levi's Jeans ran an ad campaign for their line of 501 Jeans with the tagline "Button Your Fly." This was due to the unique design of the jeans having a button-fly as opposed to the traditional zipper, and the tagline was a play on the "fly is down" phrase. {see Button up flies}

However, the situation is not always seen as embarrassing. Winston Churchill was once, while at a public function, handed a note reading "your fly is unbuttoned." Churchill scrawled on the note, before returning it "Dead birds do not drop out of nests."

Warnings

Because of the embarrassing nature of the open fly, a number of euphemistic ways to alert someone to it are used. The simplest is "Your fly is open" (or, in the United Kingdom, "Your fly's open"). In English-speaking countries, often a direct (but subtle) "Your fly is open" or "Your zipper is down" suffices. The abbreviation XYZ is also used to subtly remind the wearer to "eXamine Your Zipper." A longer variant is XYZPDQ, which stands for "eXamine Your Zipper, Pretty Damn Quick." Another commonly used warning in New Zealand, Australia, Canada and the UK is "You're flying low." and more rude ways such as "I thought you were stupid, but now I can clearly see your nuts"

Sometimes, the names of people who purportedly had problems keeping their fly up, such as Einstein, were used to signify the same situation.

In other countries, such as Myanmar, for example, different phrases indicating a cultural suitability have been created. The most commonly used in Myanmar, and also in Vietnam, is "I see the market is also open on Sundays..."