Here’s a neat little trick in case you don’t already know it: If you block someone and then unblock them, you can get them to stop following you.
I call it bucking :)
So, if you want to try and avoid all the drama that comes with blocking and just don’t want someone to keep following you and commenting on your stuff, try bucking before blocking. And if they’re persistent, you can always block and/or report for harassment, etc.
@aral you can also remove someone from following without needing to do this, there's a hidden feature in your settings where you can manage follows and followings, and you can remove any of the two