Giving examples from yesterday, although there are more.
Parent of 9-year-old DD. Get to park to meet friends and their 9-year-old DCs. DD had a Subway with her DF for lunch which included cookie. Friend brought a bag of donuts for the kids, which she brought out after they had been running about for a bit. I said DD could have one as I didn't want her to be left out while friends were having a treat/it's Saturday (the other kids had also had food before meeting). Less than half an hour later we walk past a shop. The kids all want a treat from the shop and the other Mums say they can have a giant chocolate lollypop or ice cream. By this point I say DD can't have a treat as she's just had two but she can have some fruit or bread if she's hungry. She's upset so I compromise and say she can pick something for Saturday night movie.
Cue massive meltdown from DD as she says it's hard to watch her friends have a treat. It got harder as friends got out one bag then another bag of crisps then more doughnuts for their kids after that. And because I say no, even with calm explanations to DD about different parents different rules, I get the tantrums and the stares from friends like I'm unreasonable. However the tantrum and the feeling of unfairness passes, DD says she isn't actually hungry and plays again happily.
Similarly DD walked into the shop and raised her voice to say "excuse me" while a shopper was browsing where she wanted to go. I whispered in her ear privately that whilst it's good to say excuse me, sometimes you have to wait if people are browsing and say it a bit later and quieter if you need to. In my view she's 9, so is old enough to learn social cues. Cue overreaction from another parent I don't know (of toddlers) of "that's OK, well done for saying excuse me" to cancel out my parenting approach and makes me look mean.
All my friends relent with treats and behaviour if the kids push for it. One of them called their Mum and "evil witch" when she didn't get her snack straight away because her Mum was eating, to which she giggled and said "oh she doesn't actually mean it". My DD would be on final warnings to go home with that. One of the 9 YO pulled a slate tile off a mini house. Her mum told him to put it back but because it isn't enforced he doesn't do anything. I experience this in most parenting circles. Maybe I am a strict hag? Am I outdated?? Although I'm the youngest parent in the group by six years!! What can I say better in those moments to DD?