No reader question this week, Table Manners fans: Helena has her own etiquette dilemma.

A few weeks ago, I received a mildly depressing Evite. The host lamented the amount of “plastic crap” that his previous parties had generated and urged guests to bring their own glasses. He pleaded: “If we can save from throwing away 200 barely-used plastic cups (and save me from entering the turgid Smart&Final) well, then, Sweet Jesus, let’s do it!” These days, ecoconscious types carry a reusable coffee cup around with them. So it raised the question: Is it acceptable etiquette to ask people to bring their own beer mugs to parties too?

To some, BYOC (bring your own cup) may seem over the top. What’s next: Asking everyone to bring his own cloth napkin and ceramic plate to your barbecue? While you’re at it, you could make your own toilet paper by cutting up old T-shirts, and post a sign in the bathroom asking guests to flush only “if absolutely necessary.”

But asking guests to BYOC is the most ecoconscious mode of entertaining. Granted, there are “ecodisposable” cups made of recycled and/or biodegradable materials, but they use energy and resources in their manufacture. Recycling the cups takes energy too. As for biodegradable cups, not everyone has access to composting facilities. “Unless it’s in a compost area, a compostable cup is no better than a paper cup,” points out Nicko Fusso, director of Sustainability Is Sexy, an organization that promotes reusable coffee cups.

When I went to the party, I learned that BYOC has other benefits too. I brought an old coffee mug that I did not mind losing, and discovered that when you pour yourself a vodka tonic in a mug, you end up getting a lot more of it. Soon I was having an excellent time. Plus, the kind of cups people brought offered interesting insights into their personalities. One couple had brought sensible aluminum cups. Someone else had brought several pilsner glasses, including extras for any guests who showed up sans cup. One man brought an enormous beer stein decorated with a frieze of arm-wrestling German peasants.

Interestingly, until around 1740, people happily brought their own cutlery to dinner parties. “People carried at least a knife, usually a knife and spoon,” says Sarah Coffin, head of product design and decorative arts at the Cooper-Hewitt National Design Museum and co-curator of the 2006 exhibition “Feeding Desire: Design and the Tools of the Table, 1500–2005.” Most knives and spoons folded in on themselves for ease of carrying, and were stowed in leather sheaths or cases. Fashion-conscious ladies carried their knives in what resembled “fancy evening bags,” according to Coffin.

Unfortunately, bringing your own cup is not quite so elegant. My mug was not the kind of thing I could tuck into a sequined clutch.

One solution is to purchase a plastic or stainless steel collapsible cup. (They’re not made out of recycled material, but you’ll be reusing them many times.) You can also buy wineglasses and even champagne flutes designed for camping, with a stem you can unscrew and pack in the bowl of the glass.

But I’m still looking for a truly chic, purse-size solution—the drinkers’ equivalent of the cloth shopping bag that you can scrunch into a tiny pocket and tuck into your bag. I live in hope that someone will design one. The era of the fold-up knife and spoon may have ended in 1740, but, with luck, we’re now entering the age of the collapsible martini glass.

Table Manners appears every Wednesday. Have a Table Manners question? Email Helena.

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