Fabulous meals should be paid the complement of good clothes to eat them in. For dining out in a very good restaurant, where the order is strictly dining not dancing, wear a short evening or rather magnificent cocktail dress. The important thing to remember is that only your top-half is seen above the table, so choose a dress with a flattering neckline - you're the judge of how much of yourself to bare. Sounds unromantic but delicacies tucked away behind a tiny waistband are going to put a strain upon it; it should never be too tight, for comfort's sake.
What you wear upon your head is optional; a hat adds terrific chic if it's tiny, ridicoulas and becoming. But if it falls short of any of those qualities, leave it at home.
The covering for your dress should be an evening coat, a fur or (poor you) a stole.

Ann Freeman-Sanders - The Intelligent Woman's Guide to Good Taste

Okay, I am not suggesting a return to the constrained, rigidly defined 50's standards as outlined above but...what happened to putting some effort into dressing for dinner or, at the very least, not wearing the same jeans that you went grocery shopping in earlier in the day?

I'm asking this question because the other evening we went out to dinner with a group of friends. The food and company were wonderful...I had a great time...but I couldn't help looking around the restaurant and being appalled by the sea of denim. I know that at this point I sound fuddy, and possibly even duddy, and I know that jeans can look hip or chic if worn a certain way...I love to juxtapose jeans with unexpected items...but that wasn't what was happening at the restaurant, it was just "jeans plus sweater" or "jeans plus blouse". Isn't part of the fun of going out getting dressed up?

I know that, for me, a good part of going out is the anticipation of what I'll wear. On this occasion though my husband had said "this is a casual dinner" with a certain glint in his eye (he knows me too well). So, I dressed down...and was still more "dressed-up" than 90% of the other patrons. There was one ray of hope though...a girl channeling Audrey Hepburn in a black fitted sweater and skinny pants...gold ballet flats...a big, black leather handbag slung over her shoulder...and a mustard yellow coat. Hope (as they say) springs eternal.