Dear Eric: My husband and I recently hosted the wedding of our daughter in our beautiful, upscale California beach town. The reception was described as “cocktails, dinner and dancing,” and children were not included. The dress was “Festive Cocktail Attire,” which was communicated via a save-the-date notice sent on paper via the U.

S. postal service and email. The notice was sent nine months before the wedding.

The dress code was also mentioned in the material that accompanied the invitation, sent two months before the wedding. It was a fabulous event, with great Spanish cuisine, a 12-piece live band and fun, colorful decor chosen by my daughter. With one weird exception: My husband’s older sister, a woman of 76 years, who lives in an even more upscale nearby town, but who arrived at our event looking like she had just taken a walk on the beach, in white jeans, very casual sandals, and the sort of untucked shirt you might throw on to go grocery shopping.

Meanwhile, her husband followed our dress code, as did her daughter in a lace designer cocktail dress and stilettos. This older sister was the topic of much speculation, as she stood out like a sore thumb. Several of our daughters’ friends who had, of course, dressed up, asked if she had done it on purpose, as did a couple of my friends.

I don’t know what to think, except that this event harkened back to my own wedding more than 35 years ago. In the spirit of building cordial relations, I had asked my husband’s .