On Sunday night, I took my folks to dinner at a fancy vegetarian restaurant, the kind of place where the menu tells you where all the vegetables were grown. My dad wore khaki pants and a button-down shirt and my mom wore a sparkly sweater. My brother wore shorts, a hoodie, flip-flops, and a baseball cap. I felt kind of embarrassed, like he was disrespecting the restaurant by dressing so casually, and making what was supposed to be a special occasion seem more workaday. I know he’d disagree. If you go to a fancy restaurant and there’s no explicit dress code, should you dress up anyway? Or am I being overly traditional? —Dress for Success

Dear Dress for Success,

People shouldn’t go to fancy restaurants dressed like slobs. Paying for a service isn’t an excuse to be rude, and it is rude. A lot of thought has gone into the décor and the food. Someone laundered and folded the linen napkins and polished the silver. Someone strained your black truffle purée through a chinois and cut the carrots into geometrically perfect ribbons. The least you could do is put on a pair of clean jeans.

Nowadays, fewer and fewer restaurants insist you dress up. Some restaurants state that the dress code is merely “recommended,” and even when it’s “required,” the restaurant may not bother to enforce it, particularly on the relaxed West Coast. La Folie in San Francisco, for instance, recommends “casual, elegant attire” but chef-owner Roland Passot says he doesn’t turn away the underdressed. Nor does he force them into a jacket, since it’s impossible to stock enough jackets to fit everybody. “Often it’s too long or it’s too short in the arms and the customer looks like a clown.”

In the age of jeans and T-shirts, it hardly makes economic sense for a restaurant to require jackets and ties, especially when the guy who looks like he just rolled out of bed with a hangover could be a dot-com billionaire with a taste for fine wine. Passot recalls: “I had a party of six. Five were in jackets and one was in shorts and flip-flops. That gentleman was the host, and they ended up spending three or four thousand dollars.”

But although upscale restaurants shrink from enforcing dress codes, they still prefer that you dress up. “It’s a mark of respect,” says Mauro Maccioni, co-owner of New York’s Le Cirque. Dining at a fine restaurant isn’t just about the food. Part of the pleasure is people watching, and that’s not very enjoyable if everyone looks like he just came from the gym.

Dressing with care also benefits you. If you’re spending money on a nice dinner, then taking the time to put on a special outfit is a ritual that provides a sense of occasion and reminds you—and your dining partners—to savor the experience. And depending on the restaurant, a stylish ensemble might get you better treatment. Alan Flusser, author of Dressing the Man and owner of a custom-tailored menswear store, says his soigné appearance gets him better tables at plush New York restaurants. Flusser designed the film wardrobe for Michael Douglas’s character Gordon Gekko in the movie Wall Street, and says he favors similar ensembles when visiting places like 21 or the Four Seasons Grill Room. “They always give me a good seat. They want people to see me because of the way I dress.”

So you should dress up when visiting a fancy restaurant, even if the venue doesn’t require it. It’s more important to make an effort than to follow fixed rules as to what can and can’t be worn. For instance, jeans are OK, according to Maccioni. “A nice pair of jeans and a blazer … can look a lot more elegant than a hundred-dollar suit and tie.”

Bottom line: You don’t need to wear a bespoke suit. But if your outfit is one you might wear on laundry day or to eat takeout pizza, then you should pick something else. And it’s never OK to wear sweatpants unless you’re getting your food to go.

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