I've tried this with a serial-interrupter. The danger of this approach is that most other people in the room won't remember who was speaking first. You'll get responses of "you were both talking at the same time. I couldn't understand either of you", and you'll both look like idiots.

I see you've met my mother.

But on a more serious note: I tried that too. Doesn't work with certain people. Some get even angry, give you a "Let me finish talking!" lecture and continue talking for literal hours. What i started doing, was to just leave. Like, physically leave. Now that probably won't work if you're in a meeting or talking to the boss, so use with care.

Then there is the class of people that just don't stop talking even if you physically leave the room. I know two of those, so statistically speaking either I am an extreme outlier there or there are a lot of those out there.

Currently living with the type

Leaving might work with people who are intentionally being rude.

Most of the time, people aren't aware they're being rude, but will be offended if you try a passive-aggressive way of implying this is the case.

not to mention "the other person was a serial interrupter" is often a case of "you spoke non stop via a single run-on sentence for 20 minutes and monopolized the conversation"

I understand that's sometimes the case, as I've been known to interrupt people myself. But in this particular instance I don't think I ever spoke more than 15 seconds without them speaking over the top of me. I later got them to speak about it in a more candid setting, and they confessed that they find most people to be too boring to listen to.

That sounds like ADHD

Apologies, I didn't mean to put you on the defensive. Well, I mean, I did, but I didn't mean to be mean :p

However, despite the risk of still appearing to be continuing the 'attack', it's really not about how "long" one speaks. It's mostly about speaking in a way that enables exchange in conversation, by allowing counterpoints to enter, vs not doing so, and making multiple unrebuttable statements in a row, completely monopolizing and derailing the conversation.

E.g. (Good:) "I think the government should stay off the gold standard, so that the pound can reach a level that can keep our exports competitive. [Pause]"

vs

(Bad:) "I think the government should stay off the gold standard, partly because our exports, well, you know how women are always underpaid compared to men, 70c on the dollar, which by the way would have been stronger than the pound, had only the government not treated the whole case with the federal reserve so shabilly, almost as shabbily as cryptocurrencies, which by the way are the future, only a fool would not invest, filecoin in particular; have you shared drive space to the IPFS yet?"

There. 10 seconds max. But good luck discussing the gold standard after this. Or the pay gap. Or the Federal reserve. I wanted to interrupt myself like 5 times during that sentence.

Obviously the commonest example is people speaking in run-on sentences like in the example above, but this is not the only way to make yourself uninterruptible. An equally annoying variant of this is where sometimes people actually pause at a natural point for counterpoint, but when you attempt to 'reply' or offer your counterpoint, they continue as if to say "the pause was not an invitation", effectively transforming the counterpoint into an interruption. This is one of those cases where person A then claims they were interrupted, but in fact person B could validly claim the same. This is often a display of power, as it has the effect that A 'paces' the conversation, painting a bad picture about B 'the interruptor' in the room, and causes B (and all others) to vastly delay or completely bury any further attempts at counterpoint when the opportunity naturally arises.

E.g.

  A: The report needs to be ready by Monday [Pause].  
  B: Of course, but we still need to consider--
  A: ... since any later than Monday -- excuse me, B -- will delay the whole project by a Month. [Pause].
  B: Yes. Of course. But before we submit we really should--
  A: ... and if the project is delayed -- excuse me again, B-- by a month, we'll be REALLY late then [long thoughtful pause].
  B: ... y ... yes. I do think however that it we really ought--
  A: ... and good heavens -- B, please let me finish-- if we delay, what will I tell Bob? So, we're all agreed? Good. We'd better press on too, we're running out of time. B, you wanted to say something?
  B: ... no, no. All good. Let's move on.

It sounds like you're trying to make me aware that I might be the one to blame, here. That maybe this "serial interrupter" was just trying to get a word in while I railroaded the conversation. And that's fair. I didn't give you a lot of information to go on, so I appreciate you trying to make me at least consider the possibility that I might be the one at fault. Your points are valid -- I'm not going to argue with any of them -- but I don't think they apply to me in this particular scenario.

Also, not that it's very important, but if you can read out that passage of yours in under 10 seconds I'll give you a prize!

It's good when talking one on one. I talk "through" them when they attempt to cut me off. It happened once that the other person got angry, and told me I interrupted them. When I recounted the conversation and how I had actually started first, they were stunned. It was a wonderful feeling

But this is worse because the interrupter may be doing it in good faith, as in, "I already predicted the rest of your paragraph, let's save 50 seconds of our lives."

edit: unless they're a "serial interrupter" as in sibling comment, we have one of those

The problem with this is that when they fail to predict you usually end up having to repeat the whole argument, to explain it to them the subtle difference between what you where trying to say and what they thought you where trying to say. Usually wasting more time and infuriating you.

It's better to identify those kinds of mispredictions and correct them as early as possible, otherwise the communication barrier will grow until everyone gets infuriated anyway.

I've learned to let them cut me, and then remain completely silent until specifically asked to talk again. The second time it happens, they figure it out. The third time rarely comes.

What if they just keep talking, using up all the available time, and you’re never asked to continue?

Then my point was not going to be considered anyway. That is typically the case only with exes.

Whenever I bring my axes into the conversation people seem to not want to make a point anymore.

Yes, an axe should be a blade, not a point!