Yes you can and it is very easy to do. just click the ignore button from the left site and under the every profile avatar. And if you put someone in your ignore list it will be completely private and your ignore list will only be visible to you and no one else will be able to see it. So you can feel free to put anyone on your ignore list.  For this you will not have any problem You can keep as many users as you want in your ignore list There is no limitation for ignore list