DEAR MISS MANNERS: On a small-boat river cruise my husband and I booked in Europe, the vast majority of our fellow travelers were enjoying the opportunity to explore the local cultures, foods and customs.

But unfortunately, one of them spent most of the time setting passive-aggressive traps for the crew of the boat. This person would place an order for an exotic favorite drink from back home, then berate the bartender when the presentation did not match all the details from their hometown bar. When the bartender offered (three times) to alter the drink to meet expectations, the response was, “You obviously don’t know what you’re doing; just take it away.” Similar demeaning comments were directed to the chef, the cabin attendant and the local guides.

The senior crew members did their best to step in to take the worst of the abuse. Fellow travelers were embarrassed by the behavior and wanted to mitigate the situation. At various times, we pulled the crew members aside to offer our apologies. We wanted to confront the aggressive passenger, but no one could devise a polite way to intervene. If we encounter a similar situation in the future, what would Miss Manners suggest?

GENTLE READER: No society can function without an agreed-upon code of etiquette, but the problems of not having one become apparent more quickly among those thrown together -- and kept -- in close proximity for an extended period of time.

Who, then, enforces the rules? Both the crew and the other passengers acted correctly, but it was not enough. Such efforts having failed, it was time for the captain (or some other officer in a recognized position of authority) to speak with the unruly passenger.

Any sensible captain would be happier ordering passengers into lifeboats, and may feel hesitant to intervene, remembering that the charges are also paying clients. But such is the burden of command. Judgment must be exercised in determining when such an extreme step becomes necessary, but Miss Manners trusts the captain to act before a full-fledged mutiny occurs.

DEAR MISS MANNERS: What are your thoughts on expectant mothers and fathers throwing themselves baby showers?

My friend has apparently decided that the two showers already given by friends and family in her honor did not result in a sufficient haul of gifts. She and her husband are now throwing themselves a diaper shower, even going so far as to assign each invitee a particular brand (the most expensive, of course) and size of diapers to donate to the cause.

This couple is not in need of financial assistance. Is this type of excessive gift-grabbing the new normal? I’m not sure how to respond to the invitation.

GENTLE READER: It may be the new normal, which does not make it acceptable to either Miss Manners or those who are repeatedly expected to cough up time and money. The proper response is to find that you have a prior engagement on that particular day.

(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, Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO 64106.)

DEAR MISS MANNERS: I hosted a dinner at my home for some close friends, and one texted the day before to let me know that she would not be able to attend; however, her husband would still be able to make it. They had taken it upon themselves to invite a friend of theirs named Bert in her place.

I had met Bert on prior occasions and have always been appalled at his rude manners. Anything from lecturing me about my “obesity” to arrogantly correcting anyone within earshot is the norm for him.

My friends seem oblivious to his behavior, even though it happens right in front of them. He has chased away many guests at their home, due to his sharp words. While I can simply remove myself from his presence at their gatherings (or more often, I don’t attend many of their gatherings anymore), I would not have the same option at my own table. I certainly would not want to subject my guests to his belligerent attitude.

The fact is, he is not welcome in my home. I was in a very difficult situation, since my friends had already issued the invitation. I couldn’t use the excuse that I wouldn’t have room at the table, as the wife would be absent and Bert would be occupying her spot.

I told her that I didn’t mean to be offensive, however, I needed to be able to trust that Bert would refrain from being rude to me and to my guests. She was taken aback, as she insists that he is “a sweet guy.”

I happen to know that several others have disagreed with her on this point over the years. In the end, the husband and Bert did not show up, and my friend is quite offended. I’m sure that I could have handled it better, but I’m at a loss as to what could have been said. Whenever anyone has tried to discuss the topic with her, she completely denies it and is very insulted. How could I have politely conveyed that it is not appropriate to invite someone else to my home, especially someone that I don’t even like?

GENTLE READER: The specific problem you mentioned is simpler to answer than the general problem you propose. Rather than exact a pledge for Bert’s behavior, you could have -- if you feel as strongly about Bert as you indicate -- apologized, but explained that Bert is not among the guests you invite to your home.

This creates a problem for the friend who violated this rule by inviting him, but not for you. And while the answer may upset her, Miss Manners notes that your less direct approach had the same effect. Less extreme situations require less direct answers, with a less guaranteed result: “You know how Bert is an acquired taste, and while we should definitely get together, my other guests are very sensitive and will not get his sense of humor.”

(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, Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO 64106.)

DEAR MISS MANNERS: When my daughter and son-in-law were on their way over for Christmas, they called to ask if I minded if they brought their roommate, who had no family and no other plans for the holiday.

While I did not want to be rude, especially on Christmas, I did feel like I was put on the spot. I explained to my daughter and son-in-law that while I empathized with their roommate’s situation, I felt Christmas should be more intimate and was to be shared with family. After all, this was my daughter’s and son-in law’s first Christmas as a married couple. Was I wrong to tell them to leave the roommate at home?

GENTLE READER: It seems to Miss Manners that you have a strange idea about the meaning of Christmas: that it involves excluding stranded outsiders. That is not the general interpretation. Nor is it held by your daughter and son-in-law, whose exclusivity you say you wanted to protect.

DEAR MISS MANNERS: I have wonderful in-laws, whom I adore. They are always willing to give us a hand on home improvements, which is saying a lot, as they live several hundred miles away. I consider myself lucky. There’s just one thing that bothers me when they visit, and I wonder if I should just let it go, or if it can be solved.

Both my in-laws fall asleep in the living room during the day. The problem isn’t that they sleep -- it’s that my mother-in-law, especially, snores. The sound of snoring just grates on me, especially if I’m watching something or trying to focus.

We have perfectly adequate guest rooms, with beds that are always fully made. I’ve asked my husband to suggest that they nap in those rooms, but he refuses. Is there a polite way to ask them to nap upstairs during the day, or should I just deal with it for the time that they are here?

GENTLE READER: It is difficult to remember that people do not snore on purpose, and are not even aware that they are doing so. So while Miss Manners understands the urge to smack them awake, please keep in mind that these are your wonderful in-laws as well as your guests, and refrain from doing so.

You can announce “nap time,” as if you, too, were going to catch one, and you can assure them that they will be more comfortable upstairs. But if they do not intend to nap, and just doze off, they may not move.

In that case, can you? You could go upstairs, or busy yourself in the kitchen or another room until the noise subsides.

DEAR MISS MANNERS: Some family members came to our holiday celebration and ate almost nothing. The explanation given was that they had been hungry, and ate at a restaurant before arriving. What should we do and say next time, if anything? We enjoy getting the family together, but this behavior is hurtful to the hosts who have worked hard to prepare the meal and get the family together.

GENTLE READER: Say nothing and be grateful for your extra desserts. Miss Manners does not approve of scolding even thoughtless guests.

(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, Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO 64106.)