There are lots of different ways to do this. But first you need to ask yourself: why does it matter?
Twitter relationships aren’t like buying a pet – they can just be for Christmas. Or during a live-tweeted event. Or simply over a weekend.
People come, and people go.
It’s great if you’re doing the kinds of things that make them want to stay, but losing followers is an inevitability. It happens every single day, and it’s something that you have to accept. Of course, there’s a big difference between continuously losing massive amounts of your network, as opposed to a few here and there. The latter is reality; the former is a problem.
And this works both ways, of course. When you follow someone you’re not signing a contract. If they don’t meet your expectations, needs or interests, or have fulfilled your initial reason for the connection once X has passed, then not only is okay to unfollow them, but it’s something that needs to be encouraged. You don’t need anyone’s permission – especially theirs.
And if they then turn around and complain, you absolutely made the right call.
(PS. If you really must know, some of the tools I wrote about here can help you figure things out.)