The Reason Navy Sailors Never Wash Their Coffee Cups

The U.S. Navy has some unusual traditions, but few are quite as strange as the unofficial rule surrounding coffee mugs: Simply put, don't wash them. Ever. Instead, sailors allow layer upon layer of dark coffee residue to build up inside their cups until the ceramic is stained nearly black. While those of us with OCD or mere cleaning standards might recoil in horror, the tradition been around for decades and no one has reportedly fallen ill (yet).

The practice is apparently associated with Navy chiefs and other senior sailors, as their coffee cup's appearance can function as an unofficial indicator of experience. Really, who needs medals and ribbons when you've got a "cup of joe" in hand? The grimy mug is one way of establishing hierarchy, something they're quite fond of in the military. The more "seasoned" the cup is, the more senior its owner. Just like a well-kept cast-iron skillet gets seasoned over time with continued use, a sailor's cup accumulates coffee oils and residue. 

For that reason, cleaning someone else's coffee cup can be considered a serious breach of etiquette. Online, folks reminisce about their personal experience with dirty cups while serving in the Navy. One Redditor noted: "Was in the Navy in the early 80's and one of the worst chewings I ever got was for washing my Chief's mug really well and getting rid of that coffee stain." Another added: "You clean a mug of [a sailor] it's a death sentence for that person."

It's no surprise that superstition plays a role, as water-based mythology has long been part of seafaring life. Some sailors regard washing their cup as bad luck, along with whistling onboard or setting sail on a Friday. It's not that using soap will cause something terrible to happen, but rather that the cup's accumulated grime has become associated with routine, deployments, and years of service. It's akin to seeing someone soak a cast-iron skillet after a cook has spent years perfecting its seasoning.

Believe it or not, there's also a flavor argument for letting the coffee grime build up. Some sailors genuinely insist their coffee tastes better from a gunky mug. The idea is that coffee oils left behind on the cup contribute a subtle flavor to subsequent cups. Of course, this technique only works if you're drinking black coffee. If you like cream and sugar, this Navy tradition may not be for you, since leaving either behind can lead to mold, not military distinction.

Though, not every sailor still partakes in the historic tradition. In the same Reddit discussion, another user noted that the times, they are a-changin': "This is mostly true of the older sailors from before the days of Starbucks...Ships now have Starbucks on them and COs are starting to demand covered drinks to minimize spills." While a Starbucks Crème Frappucino doesn't have the same rustic appeal of a grizzled sailor clutching a stained mug, it's certainly a touch more hygienic.