Heh... I just saw what I think is the post in question. There will be a Mary Sue reference, Read Advice for Aspiring Authors, Read the Rules, or a mention of characters being Flat and Boring, or any combination of the three in just about any given Yami Ryu post. Guaranteed.
It's actually kind of funny when you think about it.
If you're reporting something, you normally just click the little red triangle on the top-right of the post in question (make sure you click the top-right one and not the lower-right one, or you'll report the wrong person). If that doesn't work, then PM a mod with a link to the topic with the post in question. If you feel that it's severe enough and the mod isn't responding, the only thing you can really do is go to an Admin, or even Joe (Serebii) himself. Thing is, whatever Joe says goes. So that's the most you can do.