Saw this humorous topic I just have to share for comment, from the, sorry to toot their horn with this, but GTAForums' fab-tastic V section;
http://www.gtaforums.com/index.php?showtopic=524618
Note that anyone who ALREADY killed a Rockstar player in the game has this achievment you can score by taking them out, but also note, I believe they don't advertise sessions of PLAY with ROCKSTAR royalty in regular sessions of GTA multiplayer, so unlike my first guess, all the excitement of this Achievement seemed sapped down to nothing when you know this!