DEAR MISS MANNERS: My Facebook friends have wonderful lives, and I am glad for them.

They have the best boyfriend/girlfriend/husband/wife. ("Yeah, be jealous," demands one young lady about the man in her life.) Their sons and daughters win academic and sports awards and are the most thoughtful beings on the planet.

They enjoy relaxing/exciting/exotic vacations. They build huge houses and plant lovely gardens. They enjoy laughter and parties with friends and warm and happy holidays with families. Their grandbabies become more and more adorable with each passing week.

They are thankful people, my Facebook friends, wanting to express their sense of gratitude for all the good in their lives. As some will put it, they are "blessed."

How does one know when one has crossed the line between "sharing" with a hundred or two of one's closest friends and boasting?

GENTLE READER: "Sharing" is a word best used to teach small children to allow other small children access to toys. The activity it now describes teaches the contradictory lesson of It's All About Me.

It is one thing to share good news with intimates who you know will rejoice for you, and for whom you have reciprocal empathy. Shouting from the housetops, however -- especially now that one is so easily able to reach untold numbers from there -- is another.

The test Miss Manners suggests applying is what reaction is expected from the recipients of one's announcements. Not everyone is so frank as the young lady who said, "Yeah, be jealous," but that seems to be the general motivation.

DEAR MISS MANNERS: My sister was hostessing a luncheon for 12, and to her dismay, a guest showed up with her own guest, announcing to my sister, "I knew you wouldn't mind."

There was the table set for 12, which was all it would comfortably accommodate, with the china service for 12 laid out on the best tablecloth. Horribly awkward!

I think I'd have been frozen in the doorway, but my sister let them in, despite her shock, and tried to conceal that she was laying a stray extra plate at a hastily added place. To my way of thinking, the guest should have been allowed to feel the full embarrassment of her actions ... if she was capable of it. Something along the lines of, "Your guest is welcome, but now you are the extra person for whom I have no space."

Please, Miss Manners, what would be the correct thing to do in such circumstances?

GENTLE READER: The wisest thing to do, whenever someone says, "I knew you wouldn't mind," is to run. No good will follow.

Unfortunately, your sister was not in a position to do this, as she was at home with guests. Miss Manners congratulates her for behaving politely, although she deeply sympathizes with your desire to chastise the presumptuous guest.

A compromise that might squeak through as accidental would be to say sweetly to the offender, "I'm sure you won't mind squeezing in a bit to make room for your friend," and seating her diagonally with the corner of the table pointed toward her.

(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: Is it appropriate for one of my friends to text my fiance exclusively with casual conversation? They were not friends prior to our relationship. I'm not asking if it's wrong considering I do not know the situation, but rather I'd like to know if there are any guidelines that deem it appropriate.

GENTLE READER: Are you asking if it is appropriate for your friend to be friends with your fiance? Or are you asking Miss Manners to tell them to stop it?

If your fiance is texting your friend while you are trying to hold a conversation with him, then guidelines would deem this to be rude. Otherwise, you would do well to be happy that everyone is getting along.

DEAR MISS MANNERS: I am a flight attendant for a major airline. As you can imagine, I deal with hundreds of customers each day I am at work. I try to present a polished look, and I feel that after 25 years in the industry, I still have maintained an excellent attitude.

What is really getting me down is when passengers comment on how I look. Nearly every day someone will say to me, "You look tired."

I do not know how to respond -- especially when I am not tired. I do not comment on their looks, so why is it OK for them to comment on mine?

GENTLE READER: Well, it is not, but they mean it to be sympathetic. They are thinking how tired they would be if they had to do your job, and offer this as a way of being sorry they are causing you more work.

But folks, telling people they look tired is really tiresome. Miss Manners begs everyone to cut it out.

DEAR MISS MANNERS: Should I refrain from asking my sisters-in-law, none of whom I'm really close to, not to come to the hospital waiting room to wait with me while my husband, their brother, has a relatively routine surgery? One of them is just nosy.

I'm sure they love their brother, but we never associate with them, and I just don't want the stress of having to make small talk with them. It's awkward, and I don't want to be hurtful -- I just want to be alone to wait.

GENTLE READER: Yes, you should refrain.

As inconvenienced as you might feel, this is their brother, and nosy or not, they have as much claim as you to wait for him at the hospital. Moreover, they've known him longer.

The stress of making small talk with in-laws is called being part of a family. But Miss Manners will allow you this: If the sisters ask if there's anything they can do for you, you may send them out for coffee -- if you do so graciously.

DEAR MISS MANNERS: Is it OK to cut, clean or clip your nails at a table at home or in a restaurant?

GENTLE READER: Only if you are eating alone, with the shades down, at a table no one else will have to use.

(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: When my husband and I were invited to a friend's dinner party, I replied that I did not think we could arrive in time for dinner, due to a work commitment with a specific end-time, but that we could arrive after dinner if that would be OK.

The host then let me know she was frustrated that I seemed unwilling to accommodate her invitation by hurrying to get ready and getting on the road in order to arrive on time. (The travel time alone would be about 45 minutes, depending on traffic.)

Was I incorrect in replying that way? What would have been the most polite way to reply?

GENTLE READER: An invitation is not an opening bid in a negotiation. You were invited to dinner, and the correct reply was that you are very sorry, but you are unable to attend due to a prior professional engagement.

Only then would you have Miss Manners' permission to add that the conflicting engagement would prevent you from arriving before dessert. This gives your host the opportunity to amend her invitation to an after-dinner arrival, but without requiring her to do so. It would also avoid an unseemly discussion about whether your driving shows sufficient determination.

DEAR MISS MANNERS: We have been invited to a wedding and do not know the couple. We are unable to attend. Should we still send a gift or money? It is an awkward situation.

GENTLE READER: It is only awkward if you believe that strangers will be devastated to think that you don't care enough about them. Even if you did know them, Miss Manners assures you that good wishes are all you are required to send with your prompt and polite response declining the invitation.

DEAR MISS MANNERS: New neighbors, who have yet to move into their new home, have been to the house twice, feeling free to invite themselves into our yard where my children and their friends are playing.

While I am not opposed to allowing their children in our yard, we do enjoy our family time with either just my family and/or our immediate family or close friends. As a corner lot, our home is a gathering point for children, but we feel we are being taken advantage of.

I was offended when I came out of my home after dinner to find several children whom I do not know in my driveway. I feel this has got to get under control before it becomes a habit. While I do not want to offend others, we are obviously closer to some of our neighbors than others. I'm looking for the right words.

GENTLE READER: Return the offending children to their prospective home, and greet the parents with a worried look. "Oh, thank goodness we found you," you should declare breathlessly. "We weren't sure you knew that your children had wandered off."

Repeat as necessary until the parents do what they should have done in the first place, namely, ask. You can then say how much you look forward to your families' getting to know one another in due course.

(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.)