Let's put this in perspective then. It's not just rude, it's against policy, it's not just against policy, it's technically intellectual property infringement and is akin to theft and is also illegal.
So I'd say it's slightly more than rude.
That being said, this isn't the place to be posting about it, because we don't give a shit. That's between the artist whose work is being stolen, the thief, and the help desk. Or between you and the report button. But not here. And of course the person stealing work blocked you dumbass. Just report it and move the fuck on. In all honesty, unless the owner of the original art work files an offical DMCA report with DA then it may or may not be resolved after a very long period of time. But then again such is the risk of posting your work on the internet.
And fucking watermarks damnit, it's their own fault if they didn't.
Almost as annoying as that, is trying to find a reference and not being able to.
I was trying to find a simple image of a Grand Piano, just at a specific angle. I had to sort through mislabeled Upright/Vertical Pianos, a bunch of models standing in the way of pianos, and tons of pictures of just the piano keys When I finally find something, the reference picture cuts off part of the top or bottom of the piano, or the quality is so bad that I can't see even obvious details.
Typically if someone puts up something that can be used as a guide, like a stock photo or anatomy tutorial, the person who put it up requests that using their work requires a link back to the reference (this is usually the case, but not always). This is to prevent misuse or theft, and also allows it to spread so that it may be used by other people. If this is not the situation, and somebody just traced over another person's picture, then that's not cool. If you're the original artist, you can speak to the person directly or rally support to resolve the situation. If it's someone else's work being infringed, the best you can do is speak to them about it and let them handle the situation. Really, it shows a lack of courtesy and common sense when people don't follow basic guidelines.