Keep in mind that a good number of celebs don't write their own Tweets and don't bother reading anyone else's. Think Russell Simmons is gonna see that vicious comeback to his 678,453,764th motivational message of the week, let alone respond to it? Highly doubtful. And even if he did read it, he'd just do eight hours of Bikram yoga, drink an asparagus juice and get back to copying off of old Successories posters. Blocking someone would fuck up his chi or something. Find someone who clearly interacts with their fans/followers. Bill Simmons of ESPN and Grantland "fame"—who admittedly is at best a quasi-celeb—is a great one to start with.