If you fall victim to serious griefing that violates the "Big Six" (also know as the Community Standards) you may choose to report the avatar who is the violator.
This is not being a tattle-tale; SL is a mostly libertarian setting where the community polices itself. So, it's your job as a resident to take appropriate action (griefing back is not a good idea--griefers are simply better at it than most of us).
First, get the griefer's name and point the camera (or just turn your avatar) in his or her direction. Then use this option from your help menu (shown at right).
When you click the option, after getting the equivalent of an "are you sure?" window, you get this next reporting window.
Here I report the ever-violent Jezz Enoch for clobbering me with her mop and calling me a "ding-dang-dong Beatnik prevert."
For the report window, there are several menus. The little picture shows the image that will be sent to Linden Lab. The abuser's name must be filled in and you must give a summary of the incident as well the category of abuse. "Assault" seems a good one in my case! In the big text box, you can copy/paste any chat or IM that supports your report or give a more detailed account of what happened.
Scavenger Hunt Bonus: 50L for the first of you to find a mop bucket and post a snapshot to Koinup of you using it or standing by it. No abuse required to win the 50L. The mall pictured has moved, I think, since 2008.