DEAR MISS MANNERS: One sends out an RSVP invitation with a specific deadline, and then, because of poor response, the hosts want to cancel. Obviously the regrets do not need to be notified. Those accepting the invitation should be notified.

A topic of debate within my household: Is the host under any obligation to notify those who did not respond?

GENTLE READER: Your implicit frustration with those who do not respond to invitations would normally find a sympathetic listener in Miss Manners.

But she finds herself wondering instead about the "poor response" you cite in justification of revoking an invitation that has been both issued and, in some cases, accepted. To these people the host owes an apology, an explanation and, ideally, a replacement invitation.

Given how many people are in the habit of attending events to which they did not respond, it would be wise to warn the non-responders as well, lest they appear on your doorstep expecting to be fed. In fact, you do not need to offer to feed them ever again.

DEAR MISS MANNERS: I was invited to a dinner party hosted by my law school professor. It was on a Thursday evening and the invitation said dress was casual. I, and other students, wore jeans and a casual shirt.

I overheard the host discussing our outfits as uncouth and that we should have been wearing "business casual" attire. I was embarrassed and put on my cardigan.

Was I wrong for dressing casual? Should I have interpreted a dinner party "casual" to mean business attire?

GENTLE READER: Has the factor of context never come up in your law classes? Or the question of what the understanding of a reasonable person would be?

Actually, nobody knows the meaning of "casual." As far as Miss Manners can tell -- and she is as reasonable as one can reasonably be -- it merely tells people that they don't have to make any effort they don't feel like making. So some feel like making the effort to look polished, and some don't feel like making much of an effort, if any. Certainly, a reasonable student would interpret "casual" as meaning jeans.

But your professor seems to have trouble understanding context. Correcting students when they are taking his courses is his job. Disparaging his guests when he has invited them to a party is rude.

DEAR MISS MANNERS: I just turned 12, and my friends were very nice, brought balloons, cookies, etc., to school. The next day, several of them asked me what I had gotten for my birthday.

I told them the truth -- that it had been a pretty busy night and I hadn't opened them yet -- but I couldn't help but think that the question was a little tactless.

What if, in this economy, my parents couldn't afford a lot of presents? It seems almost parallel to adults asking each other how much money they make. Am I wrong for thinking this, and what would be an appropriate response in the future?

GENTLE READER: The difference is that your friends are not really asking for the complete catalog you are envisioning. Miss Manners assures you that they are expressing a conventional interest that can be answered with a conventional response: Express enthusiasm for all the wonderful gifts and name one, without suggesting that it is the best.

(Please send your questions to Miss Manners at her website, www.missmanners.com; to her email, dearmissmanners@gmail.com; or through postal mail to Miss Manners, Universal Uclick, 1130 Walnut St., Kansas City, MO 64106.)

DEAR MISS MANNERS: Last week I joined a popular online dating site and went on a first date. He picked me up at my house and took me out to dinner. Unfortunately, from the moment he opened his mouth, I knew we would not be compatible.

I spent the entire evening with a pleasant expression, feigning interest, and counting down until I could go home. He had a good time, and upon following up was shocked to hear that I did not share his feelings.

In retrospect, I felt trapped and helpless on the date and wound up pretending everything was OK.

Is this the appropriate approach, or is it better to be upfront with my feelings and save us both time and the emotional runaround?

GENTLE READER: An activity that used to have the charming and perhaps fanciful name of courtship has become so businesslike that there is a frightening logic to your suggestion.

Yes, announcing, "Sorry; you won't do" at that moment when the gentleman first opened his mouth would have allowed you both to move on to the next candidates. But at what horrifying sacrifice of the decencies of social behavior?

Miss Manners is no advocate of dating services, but even she can recognize that you violated its implicit cautions. You accepted a dinner date with a stranger after -- at most -- a week of the usual preliminaries, such as exchanging emails and eventually arranging a short meeting on neutral territory.

Having made that commitment, however, you were obliged to see it through. At what point do you think you could have bolted? On your doorstep, when he introduced himself? During the soup course? Or the dessert?

The proper dismissal would have been at the end of dinner, when you express regret that you have a full schedule in the foreseeable future.

DEAR MISS MANNERS: My son is proposing tonight. I want to send her flowers tomorrow. What should the card say?

GENTLE READER: "I knew about this before you did, and preapproved you"?

Not a good idea. Miss Manners certainly favors welcoming a bride into the family, but recommends allowing the couple to break the news to you together first.

DEAR MISS MANNERS: Please tell me the proper way to open a cracker package in a restaurant. I know using your teeth is probably not right, but I don't know the proper alternative.

GENTLE READER: Why is traditional etiquette constantly charged with setting mealtime traps, when all it does is to provide sturdy utensils for consuming food?

And meanwhile, establishments that expect diners to cope with paper and cardboard have people like you assuming that propriety is legitimately involved.

There is no proper way of dealing with trash on a properly set table because it shouldn't be there. Miss Manners realizes that restaurants are required by health laws to present some items in their commercial wrappings, but that prevents them from being models for correct service.

However, she does agree that using your teeth is not an attractive solution. If the designated "tear" part of the packaging doesn't yield, as is so often the case, she recommends attacking it with knife edge or fork prong.

(Please send your questions to Miss Manners at her website, www.missmanners.com; to her email, dearmissmanners@gmail.com; or through postal mail to Miss Manners, Universal Uclick, 1130 Walnut St., Kansas City, MO 64106.)

DEAR MISS MANNERS: How would one interpret an invitation that states, "This is an adult-oriented event. Chaperoned children are welcome"?

GENTLE READER: "We really don't want children at the party, but if you bring them anyway, they'd better not be loud or break anything."

DEAR MISS MANNERS: I take the train to New York City to work and the ride is approximately an hour. Yesterday a man sitting next to me played with a bunch of coins the entire time -- moving them from one hand to the other, making an annoying noise.

Because the train ride is relatively short and I don't feel it's my place to ask others to stop, I said nothing. But if the train ride were, say, two hours, I would have lost my mind if I hadn't asked him to stop. Does the duration of the infraction affect how impolite it would be for me to ask the man to stop?

GENTLE READER: No, only if your mounting irritation might make your reaction uncivil. If you find the noise unbearable, try gently warning the gentleman that especially in New York it's never a good idea to draw attention to one's money. If he's a true New Yorker, he will be so wounded by the insinuation that he is not a native that Miss Manners trusts he will be silenced into submission by the shock.

DEAR MISS MANNERS: My younger brother is half-African American. His fair wife is Anglo-Irish. They have three small sons, all blond and blue-eyed.

My brother takes them out on Saturday mornings so his wife can sleep in, and as no good deed goes unpunished, on these outings he is often accosted by strangers demanding to know the parentage of the children and denying they could possibly be his. He is usually quite patient and good-natured, but occasionally the queries become vehemently accusatory, as if he is suspected of abducting the wee laddies and nefariously nannying them in the coffeehouse, grocery store or park.

One never wishes to be rude, and so one turns to Miss Manners, to seek an effective rebuff.

GENTLE READER: If these inquiries are becoming attacks, your brother would be more than justified to say, "I'm sorry, but you are upsetting my children" as he changes seats or hurries the little ones off in another direction. This should make it obvious that it is the accusers, and not he, who is the real threat to his children's well-being.

As a side note, Miss Manners can't help but caution you against the mindset that refers to a fatherly outing as a "good deed." A parent does not baby-sit his own children, but one who thinks he does could well lead others to suspicions of his being a stranger to them.

(Please send your questions to Miss Manners at her website, www.missmanners.com; to her email, dearmissmanners@gmail.com; or through postal mail to Miss Manners, Universal Uclick, 1130 Walnut St., Kansas City, MO 64106.)