Small stories related to dress codes:
In my limited experience with dressy occasions, I assume a wedding is an occasion where one is expected to put a bit of effort into one's appearance. The weddings I had been to until that point were evening occasions where a nice LBD, a pants suit, suits and ties were the norm. Enter my short-notice invite to an afternoon wedding in the early spring, when it was still chilly outside. I don't recall any dress code being specified, but my brain went immediately to "It's a wedding, dress up", and I ended up in a simple black sheath-dress, hose and heels with a large scarf worn as a shawl to keep my shoulders warm.
Queue my surprise when I showed up to the church for the ceremony, entered the sanctuary to find probably 80% of those in attendance were in old jeans, baggy sweatshirts and sneakers. I felt entirely overdressed and out of place, along with being appalled that anyone would think sweats and sneakers were appropriate in any way for a wedding. The bridal party was dressed up nicely. The simple ceremony was followed by a buffet-style dinner at a local prom hall, then it was over. No dancing, nothing.
I grew up and live in a large metropolitan area, moved to the outskirts of a town of 1200, and was called for jury duty in the small town I had lived in for about 1 year. The summons said something about it being a courtroom so to dress/behave respectfully. Thinking courtroom = business casual, I hunted through my casual wardrobe for something appropriate. My local friend assured me things weren't as fancy as they'd be in the big city, and I chose black jeans, nice plain long-sleeved tshirt, and simple black lace-up shoes. I was the most dressed-up person there until the lawyers showed up in suits. Some ppl were in jeans, some in pajama pants, some wearing John Deere hats looking like they'd rolled through the dirt on their way to court.
I took part in a flash-mob at a black-tie affair. We were instructed to wear "business casual" as to blend in better. It broke my brain, as I was under the impression that "black tie" and "business casual" are very different things. As it turned out, my DD and I in our LBDs with simple cardigans and accessories were the best-dressed of the mob. One family actually turned up in ripped jeans, baggy graphic tshirts and baseball caps.
As it turned out we spent more time getting dressed up than participating in the mob, so my DD and I went out for dinner afterwards.
On topic: As we've discovered throughout this thread, regional/cultural differences and/or inexperience, as well as times changing and traditional assumptions for appropriateness possibly not fitting anymore, make dressing appropriately for an occasion a little more challenging. I feel if an occasion calls for a certain type of dress, it should be clearly stated so as to be understood. There will likely be someone who doesn't care and will wear whatever they want anyway, but for those who would rather "blend", being clear what is expected is a great help. That said, rather than "no ties, no jeans", I'd perhaps have said, "Ties aren't necessary, but please, no jeans."