Outside of bad manners, I think perhaps she just doesn't have good social skills. How does she behave in other social situations?

The slang for it is "ghosting". It's rude, but there are worse things.

Maybe she has some type of social anxiety, and when she's had enough, it's time for her to get outta there.

We at least say good bye to either the host or hostess if the other is occupied otherwise. It does seem rude to leave without a thank you.

To me it's not a big thing though. Just her way.

Do you think she doesn't know she should say good bye before leaving? Does she know that people see this behavior as rude? Maybe you should risk hurting her feeling and mention it to her. If she's hurt/embarrassed... she'll heal. If she's doing it to make some sort o statement... at least you know?

Is she leaving earlier than the majority of the guests then? It's a little strange, I wonder if she feels compelled to just slip quietly out and for some reason doesn't want to call attention to her departure. If I were having to leave early, I might forewarn my host/hostess, and I'd tell DH on my way out, I'm leaving now to 'xxxxx', or leaving now because 'xxxxx', see you at home later.

I can't imagine leaving early - or later - without thanking my hostess for having me. saying something nice about their efforts, and if at someone's home, making the offer to help clean up, package leftovers to chill, do something helpful, somehow.

Not something I would do, as it is very rude. As this is her habit, and everyone seems to accept it, I'd let it go.

Does she join in on the fun and conversation when she's there?

Maybe she suffers from something like severe anxiety or irritable bowel.

Maybe she doesn't want to draw attention to herself by making a public goodbye? Weird though that she doesn't even tell the partner she lives with she is leaving.

Or ADD? We had a neighbor who would just walk away from a conversation while in a group. We thought it was odd. Their son was diagnosed with ADHD and he had himself tested.

Sure enough he was diagnosed with ADD.

I would suggest the same as Snidely. I suppose if one were the host/hostess, one could question the guest to see if something was wrong or upsetting to the guest. Otherwise....Let it go!

Well if she wanders off leaving the man she's living with behind, it's obviously something specific about her. You could ask her? Perhaps she gets overwhelmed by a crowd and feels the need to disengage. I know a guy who does that, who will just go sit in a corner or something (not leave without the people he came with). If it's a place where he feels really really at home, he might even go lie down on a bed. He feels like he should attend the large parties, but he'll tell you he doesn't like to be around more than 3-4 people to socialize. He's not good at the saying of hellos and good-byes either, but he does do it. In our circle everybody says good-bye to everyone else (individually), not just the hosts, unless they'd be disturbing people (at which point only to the people near them, and the hosts, or leave a message of thanks with someone if it would make a disturbance to speak to the hosts).

Since it's accepted by everyone, I have to wonder if it even qualifies as "rude". The only ones bothered aren't even involved. No harm, no foul in this case.

I can't think of a reason for it. There's been a time or two I've left an affair without a scene but usually will thank the host. However it doesn't sound like she had the reason(s) I did so that's of no help. Perhaps she calls the host later for the thank-you. Or maybe not. Could be naiveté. Could be any number of things I guess. I have no explanation. Seems strange she doesn't tell her partner, but if they're presumably driving separately it must be expected. I guess I'd ask her and find out why. Since she's a friend, that's the best source to find out why she does what she does.

My husband is a very weird character. I've never known him to leave someplace without at least telling me, but I can easily see how someone would do it. Rude? I don't know. Other peoples quirks don't bother me.

I don't think I would ask her about it. She may feel anxious at the next event and not even make an appearance, if that's important to you.

I'm certainly not bothered by it. She's known to do this most of the time and everyone accepts it. I just find it a bit odd but I imagine, I have some behaviors that others find strange. She did say earlier in the day that she needed to leave early so maybe she figured that was all that was needed.

I wouldn't ask her about it. She is normally not comfortable in new situations. This wasn't a new group of people from who she normally sees. However, we have never been to this couple's home. I was just wondering if anyone else has ever encountered this.

I have an inlaw who doesn't say anything, just leaves. He has some health issues that can make him suddenly ready to leave, and when he is ready to leave he does. But i suspect it was that way before any health issues. He just doesn't feel the need to announce that he is leaving, and already talked to people while enjoying the party itself-atleast that was what he said when I asked him about it. Never considered it rude, it's just the way he is.

I've actually slipped out of large gatherings without goodbyes because I don't want to disturb the hosts or be the cause of the party breaking up early - people see others leaving and think it must be time to go. I always email or call later and explain that I had to leave, but didn't want to disturb the hosts while they were still entertaining. I still thank them via a note or phone call.

Maybe goodbyes are hard for her. Does she suffer from panic or anxiety disorders? She might be really shy and finds it hard to say goodbye and break away. We have all experienced an overly long goodbye and I personally find those to be very awkward. If I could get away with slipping out of a party or function without having to go through that, I probably would try.