The soft next means walking away for a day or two to show a girl you will not tolerate her behaviour. This only works if you don't life with her. If you live with her (or are married to her), this simply doesn't apply because it doesn't work.
Complaining, bargaining, shouting, explaining, logic and arguing are all useless counter-productive low-status behaviours that make women double down on the behaviour and do more of it because they like your low status behaviour: it makes them more secure in the relationship. The louder you shout and the more upset you get the more you CARE about the relationship. The more you NEED her. Women LOVE this. They dislike conflict, but love the security of seeing how hard you'll work with her to try and stop her doing some trivial (to her) behaviour. Giving her attention, showing how desperately you care, showing her how much you will try and make the relationship work. They love it..... but they don't respect you for it: it's killing attraction with every passing second.
Instead you do a soft next.
Concrete example: girl is nagging you, but it could be any other bad behaviour. Here's how this plays out, and I've done this many times so I know exactly how it works:
Girl nags.
MattyAnon: "You're nagging me, I don't like it. It needs to stop, and it needs to stop now."
Girl nags, because she has to test this boundary to see if I'm serious. She doesn't know what's coming.
MattyAnon: "I told you not to nag". Then I quietly and with no emotion grab my stuff and I walk out of the bar / the party / her house. It's vital that this is done emotionlessly, calmly. You express the problem, and you leave. You don't SAY you're leaving, you just go. If she doesn't see you leave then so much the better, eventually you'll get a text "Where are you? did you leave?" and you simply say "You nagged I left". THEN IGNORE. You don't want to get into explaining any more than that. Women love to try and negotiate around consequences and call you names and get a reaction. Ignore all of it.
The first time you start to do this, she'll beg for you not to leave when she sees what's happening.
Girl: "but but... I didn't know you were serious" (translation: I didn't know there were consequences) " ... please please I'm sorry I won't do it again".
MattyAnon: "um... I don't know.... I've had to ask you twice...."
Girl: "I'm really sorry, won't happen again".
MattyAnon: "well.... I guess.... um...... ok then, we'll see how it goes".
It's important not to be too easy a pushover on this. She has to FEEL that she almost lost you. And notice I don't fully commit to not leaving.
This whole scenario WILL play out again. And the second time you have to do this (for ANY reason) you don't accept any apologies, you walk out. She has to learn that she can't just talk you out of leaving when she fucks up. She has to learn that the consequence are real.
So the second time it happens: you silently pack up and you leave and you DO NOT ANSWER HER CALLS OR TEXTS. Let her stew for 48 hours. Then carry on like nothing has happened. She almost certainly won't give you shit about it, she'll be relieved you're back. If she nags, whines, complains or criticises you ...... then you do the same again. "Look girl, I don't need to hear this, you need to stop this nagging". She'll stop. If not she's on a 4 day time out. If that's not enough then it's time to move on to girls who know how to behave.
Another subtle point: she flakes on a date. You don't do anything AT THE TIME, because she clearly didn't want to show up. The time to make your complaint is when she next WANTS something, eg to meet you again. She flakes, you ignore, she tries to meet up again and you say "No.... you didn't show up last time, I'm not going to waste my time again". If she drops it, you drop her. If she persists you agree a date that is favourable to you: near your place, somewhere you are anyway, she picks you up, etc. There have to be consequences to her bad behaviour, and your absence is the best way to express your displeasure.
You inexperienced young bucks out there: do not accept offers of crazy monkey sex in exchange for forgiveness. Your high status behaviour will usually trigger a spike in attraction and need in her and she will usually try to use sex to talk you out of it. The sex will wait and it will be better once respect for you has increased. Don't accept sex as an apology or as a bargaining point. Just say "your bad behaviour is such a turn off" and walk out.
What to do for 2-4 days while she's stewing? Anything you fucking like, but especially looking around for better options and enjoying some peace and quiet away from her.