It's called Intrusive Thoughts, and apparently most people have these:

London psychologist Stanley Rachman presented a questionnaire to healthy college students and found that virtually all said they had these thoughts from time to time, including thoughts of sexual violence, sexual punishment, "unnatural" sex acts, painful sexual practices, blasphemous or obscene images, thoughts of harming elderly people or someone close to them, violence against animals or towards children, and impulsive or abusive outbursts or utterances.[6] Such bad thoughts are universal among humans, and have "almost certainly always been a part of the human condition".[7]

When I first read this, I thought "woah, that's kinda weird and worrying". Then I realised I do something similar. I sometimes rehearse violent confrontations in my imagination.

I've been involved in a few violent confrontations as an adult, and they're nothing like you imagine them to be. People like to imagine all the badass things they would have done in those situations, but when you suddenly find yourself in a brawl, your thoughts are generally "what the hell's going on here? Is this really happening?" I've heard accounts of highly trained martial artists experiencing the same thing. Even if you're physically prepared for a fight, you're not necessarily prepared for the social situation of a fight.

I assume that when I imagine violent first-person scenarios it's some sort of long-term rehearsal process where I'm psychologically preparing myself for conflict at some point in the future. I generally try and avoid situations which have a high risk of physical conflict, though, so my sample size is so small as to be useless when trying to figure out if it does any good.

For example, I recently asked a friend why she felt the need to buy a new dress for every 'special event' (galas, dances, etc.). After some thought, she said it's most likely because she will be looked down upon by other females if she is seen wearing something that she has previously been known to wear. I asked why again, and she said that sort of judgement has probably been inculcated in the majority of females; she clarified that she only bought new dresses so as not to be thought of as low status, and has no qualms wearing the same things around family.

Men have comparable status competitions and nastiness, it just isn't about clothes.

I'm surprised that nobody has mentioned this one, but it's often inappropriate to hang around with people while not engaging in whatever activity they're doing. Don't sit in the stands at a football game reading a book, don't watch TV while your friends are playing Dungeons and Dragons, don't have your headphones on while friends are having a conversation.

For many people, alcohol raises talkativeness and lowers inhibition, so you're more likely to say things you normally wouldn't (in vino veritas). Sharing private things is a friendship-builder (HPMOR 7), but it can also be embarrassing. Drinking is a pre-commitment to build friendship through potentially embarrassing interactions, and when you abstain, you're saying, "I'll hear your secrets, but keep mine, thank you very much," which is a suspicious and untrustworthy kind of stance.

To the extent the above is true, it's too bad, because

1. Some people really don't like drinking, and alcohol doesn't make them more sociable anyway
2. No one should need to self-handicap in this way to trust and be trusted
3. It's a pre-commitment, limiting your options

I think this is mostly the impression of moral superiority people get from non-drinkers. If you excuse yourself for medical reasons, or imply you're a recovering alcoholic, people will mistrust you a lot less.

I don't know, of course, but if my cohort regularly engages in a habit that leaves us at a physical and cognitive disadvantage, it really doesn't seem too surprising that we will also develop associated habits that prevent others who are not so disadvantaged from engaging with us.

Simple tradition, I expect. In many situations and cultures, consuming alcohol is simply the done thing, and not doing the done thing a surefire way of standing out. I'd also guess that people who drink in these situations expect everyone to know the social norms and agree with them (even if it's only an unconscious background assumption), and so they'll see not wanting to drink as wanting to stand out. And you know what that means.

I don't drink, don't like trying to hold a conversation over loud music, and don't like starting conversations with strangers if I don't think we'll have anything in common. Why the hell do I go to bars?

1) Everyone else is there. It's a Schelling Point for non-specific social activity.

2) It's public. There are a whole host of complicated hospitality / power dynamic / pragmatic considerations that come with inviting people to your home, or being invited to someone else's. Bars take responsibility for all the trappings of hospitality.

3) It's a ubiquitous venue. In an urban area you'll always be able to find a bar in walking distance, whereas you can't say the same for a park or a museum.

4) It's a designated area for social interaction. If I did want to talk to a stranger, this is permitted in bars, whereas it's prohibited in most other venues. (Your mileage may vary here; The UK is a lot more staid about these things than the rest of Europe and North America.)

Disclaimer: these are only the reasons I go to bars. In no particular order.

1. To exploit alcohol deals -- it's sometimes possible to get alcohol at a bar cheaper than retail price (including tip and cover). Presumably it's a loss leader for something else, or the bar is exploiting some sort of bulk discount.
2. I've observed plenty of mating/courting behavior at bars, but since the bars in my area are mostly not-gay bars, I don't go to bars to find mates.
3. To enter a kind of disassociated, free-flowing mental state brought on by the right combination of dancing, inebriation, and music. It's quite cathartic when the stars all line up correctly.
4. To sing karaoke and not feel self-conscious about it.

I have frequently stopped responding to people because I failed to respond immediately, and then forgot that the conversation existed. I have no idea how common this is.

It's been my experience that people who want a reason for disengagement primarily want that reason so they can argue it is incorrect or can be overcome.

To answer this more generally, instead of in example form people often have anxiety around social interactions particularly those they anticipate to be uncomfortable, conflict-ridden or dramatic. In a dating context (which is usually when this sort of thing happens, in my experience, but maybe you have something different in mind) it is usually a way to cease dating or flirting with someone without having to explain to them that you aren't interested. It avoids the tension involved in waiting for the person to react, the drama of any fallout and the awkwardness of spending any time interacting with them after you've dumped them.

I guess I'm volunteering to answer these things, heh. Well, other people need to answer these things too, right?

Well, so I did stop talking to my most recent ex-boyfriend. The thing was that after our relationship ended many of my friends confided in me that he and I were of vastly different social statuses, and that our relationship had lowered their opinion of my status.

Then, some months later, he returned some of the things he had of mine, and during that meeting he was exceptionally creepy. I realized that talking to him further would only increase the creepiness, and so I stopped talking to him altogether. Most recently, he replied to a throwaway tweet of mine, and I intend not to respond to it because it's still clear that he's still seeking a relationship I'm no longer interested in.