Firstly, I'll explain a "flame". Let's say I'm a juvenile arsehole with an attitude and too much time on my hands. I read your story (or pretend to) and the leave a review that says something like: "you'er storey SUX! my gmother could rite better than that and shes ded!" Note the poor spelling, as most of these morons border on illiterate. That's a flame, where they simply rip into you or your story with little reason other than to annoy and/or offend, usually trying to bait you into retaliating so they can start a massive argument (a flame war). There's no constructive criticim, simply abuse. We don't tolerate that. On the other hand, some people take any kind of criticism as a flame, no matter how nice and constructive they are about it. That's not a flame, simply constructive criticism.
Now, where to report it. If you go to the archive, down the very bottom of each page is a link that says this: "Report Abuse or TOS-breakers on the Site." (TOS stands Terms Of Service, in case you weren't sure). That link lets you send an email, where you state the problem and provide links to your profile and where the problem is, such as the page where the abusive review is. The mods will then take care of it for you.