I totally agree with your comment that dressing down diminishes an occasion for others. Many years ago, friends of ours hosted a New Year’s Eve party. The wife made it clear that she wanted everyone to be in Black Tie. Very hard to do on short notice, but most people made an effort to dress up — at the very least, jackets on the men and dresses or sparlky jackets on the women. Except for one woman, who was a friend of the husband, who told him in advance there was no way she was dressing up for a party at someone’s house on NYE. She showed up in corduroy pants and a Christmas sweater. And was completely unapologetic. I thought it was incredibly rude. It also pretty much wrecked the friendship she had with the husband, because there was no way his wife was ever going to speak to her again!
SO rude. Why go at all then?