I've been thinking a lot about the term "constructive criticism". I've had some people accuse me or others of using as a shield, essentially labelling any disagreement as harassment and thus using it as an excuse to ignore it, and while that isn't true (we don't get to "ignore feedback" for made up reasons, ultimately players either like it or they don't), I do think it's quite an important distinction to draw.
For me, and looking at the behaviour patterns of other people I don't think this is unusual, the question isn't really about whether the feedback is "constructive" exactly, it's simply about whether it's rude and whether it's personal. Obviously the more detailed the feedback the better, but even a simple black and white opinion is "constructive" when we have enough of them to gather a general impression.
TLDR it's fine to say you don't like something, just don't be rude and don't make it personal.
I'll try to give an abstract example. Say I've shipped some content. Typically we'll see quite a lot of different responses:
"I love it" or "I hate it" - you could argue that this isn't constructive because it doesn't explain why, but a raw opinion is still useful when you see them in aggregate. If there's a clear majority one way or the other, or even a very mixed response, that's super useful feedback. Obviously we'd prefer players loved it, because we want people to like our content, but that doesn't mean we're entitled to compliments. I would never try to claim that someone not liking something is "unconstructive".
"I love it for " or "I hate it for " - this is generally what people mean when they say "constructive criticism". If you've explained why you like or don't like something, then we can take that into account in the future. It's slightly tricky sometimes in practice because opinions are opinions - players disagree about stuff and even if there's a consensus on whether something is good or bad, there's rarely a consensus on why it's good or bad. I mention that to say that listening to constructive feedback isn't the same thing as immediately implementing everything everyone says - we have a lot of factors to account for in every decision we make - but this is by far the best way to get heard, even if it doesn't produce 100% reliable results. Again devs would rather hear that they made someone happy, but speaking personally negative feedback telling me what I can do better is how I improve, so I'm always happy to see this.
"This is sh*t" or "this is sh*t for " - this is where it starts to get difficult. I think we've become accustomed in online discourse to treating "I hate it" and "it's sh*t" as essentially synonymous, both just ways of expressing dislike for something. Even I do it, and I'm here complaining about it, but I can assure you as the creator on the other end, they don't feel the same at all. Saying "it's sh*t" isn't just a way to emphasise that you really don't like something, it's being actively rude to the person who created it. I'm not telling you you can't communicate this way, but if you want to interact with the creators of something, this isn't the way to do it. Even if you're very clear in your reasons, you're putting up a wall of hostility which discourages someone from engaging with you further. This is where feedback becomes "unconstructive" - I would like to respond to negative feedback where possible by either offering an explanation, or asking for more information, but by framing your feedback in this way you're signalling to me that you're not interested in having that discussion, and that I'm likely to get back a barrage of further rudeness if I try.
"The dev is lazy" or "The dev is incompetent" - this is where it gets personal. This level of discourse is simply unacceptable, and just in general I would discourage people from thinking in this way. Unless you're someone's manager, close friend or family member, you simply don't know enough about what's going on in their life to be able to make this judgement. Maybe you're right and they simply didn't care, or maybe there are a hundred other factors going on personally or professionally which you know nothing about. Maybe their family member died. Maybe the compromise they came to actually was the best option available. Maybe they were assigned a task they have no experience in (which is a fault at Jagex but not with the dev you're actively insulting). Maybe the dev agrees completely with you, and fought for that perspective, but it was ultimately out of their control. Maybe the dev understands the topic better than you. We've had projects go badly because the developers involved were actually fired in the middle of the project, and someone else had to pick up the pieces, and then got eviscerated by the community afterwards. Even more so than the previous type of feedback, this is the sort of thing that actively drives devs away from interacting with the community. You might have some twisted ideological justification like "a bit of tough love is what they need to understand how wrong they are" but in practice, and especially on the internet, people can simply walk away and don't have to put up with this sort of abuse.
A lot of people in this thread are posting things like "maybe they should get thicker skin" or "maybe if they can't take the internet they should stay off it" and ultimately that's the whole point of the thread. You don't get to determine for a dev what level of harassment they should have to tolerate. If you want them to actively participate in the sub where they can and answer the questions they have the ability to, then you have to avoid actively harrassing them, no matter how justified you may feel it is. I constantly come across questions here I'd like to answer, and when I do I get a lot of responses asking "why are you answering this and not this other more controversial question?". Eventually I just stopped answering questions, because it wasn't worth the hassle.
EDIT: Spelling.