I've heard it said that it's impolite to talk about someone on Twitter without addressing your comment to them by using their handle, prefaced by an @. I disagree. If you're going to call someone an asshole, it's impolite to address it to them. If you're objectifying them, saying something you wouldn't say to their face -- then don't say it to their face dammit. :-)
I know because I'm sometimes on the receiving end of this.
Oh that @davewiner, he's such an idiot.
I would much prefer if they left the @ off it. Otherwise I have to look at that idiotic thing over and over until it scrolls off. If you think it's going to get a reply, no way. And if you think I give a shit, I don't. It's just annoying to see a bit of stupidity staying there, like a turd in a toilet that someone refuses to flush. So I usually just block em. :-)
Sometimes it makes sense to say something about someone you wouldn't want them to see.
For example. The other day at lunch I was saying that Carmelo Anthony, the star of the Knicks, is never going to lead the team to a championship. I wouldn't want Anthony, a fine player, and a nice guy, to see that. I doubt if it would motivate him. And sheez it's not his fault he's in the same division as Lebron James (or for that matter occupying the same NBA as Lebron James). Even Kevin Durant, who is a great leader and player, and totally capable of being a champion, probably can't overcome the audacity and tenacity of the Miami Heat. At least not for the next few years.
So I vote for leaving off the at-sign if you're saying trash about a celeb.