My pet hate is parents who don't use the word no to their children. Wtaf?
TBF, I think this one is really weirdly misrepresented or misunderstood.
The idea behind it is to avoid sentences like "no running" "no hitting" "stop throwing your food" and replace them with the instruction of what you actually want them to do, like "wait, we're by a road" "come over here and play with me"
This is because if you keep saying "no doing this, stop that, don't do the other" well it's like saying "don't think about an elephant" - it gets you exactly the result you don't want.
It's more effective to tell somebody what you DO want them to do, and this is especially true for young children, if you say to an adult "don't touch that" they can instantly fill in the blanks - oh, it must be something precious, private, it might be dangerous/unstable, and they would automatically stop before they ask why. But a young child has much less developed impulse control. If you tell a 4yo "don't touch that" they will quite frequently continue to touch it WHILE asking why, because they haven't got that inhibitory control down yet. Whereas if you say something like "hands on your head" (especially if you've trained this like a game) they are already not touching whatever you want them to stop touching, so you're ahead of them and then you can either steer them away or block access or start to explain the why if you need to, and this is much nicer and more pleasant of an interaction than one where you get annoyed with them and bark at them because they haven't instantly stopped.
Also, we know that praise/reward is way more effective in cementing habits than fear of punishment is, so if you want something like that your kids don't run in the road, the most effective way to do this is to remind them/ensure that they stop at the edge and hold hands and praise them for doing that. This is much more effective than waiting until they have already run in the road and then smacking them for it.
The other concept around not saying no is about being more accepting and positive in general. It can be really easy to say no all the time to requests to play, to have something, to do something that requires effort on the parent's part and if you make an effort to say yes more often to these things then you can end up having some really lovely experiences that you might not have had otherwise. (This won't be right for everyone. I think there are some parents who already say yes too much and should say no more, instead - it needs to be a balance.)
But anyway in both of these concepts it's not a total ban, it's more of something to try and do less and do the alternative more. If people are taking it to an extreme then that's really on them, but I don't think it's ever been recommended by any expert.