Funny I'm on Twitter and I see very little rudeness. Must depend on who you follow. I don't tend to read other peoples conversations mind.
If I was a celeb I wouldnt bother with twitter, but I get that celebs want to use it to promote themselves, surely they know they're gonna get some morons/nutters tweeting them. Why not just ignore it? Can't understand why they use it for such personal stuff rather than a professional tool.