I don't believe we,Christians, (those who make a habit of becoming more Christ-like etc.) are sinners because we don't purpose in our hearts to continually sin. We WERE sinners who have been saved by grace. Yes, we may have areas where we struggle and fall into temptation and commit a sin. However, we are able to confess, repent, and be forgiven. I don't think God is in Heaven calling us His "sinners saved by grace." Another way I look at it is from the perspective of a parent. We teach our kids to discern right from wrong so they won't grow to be bad children, teens etc. But even the most well-mannered child, armed with that knowledge, will do something bad from time to time, yet their parent won't say "hey i have a bad kid because they did xyz." Ultimately they're good because they strived to do so, but they slipped up. They learn from their mistakes (hopefully) so they won't slip up again, and keep it moving. It's the same with us Christians. God takes into account our flesh and knows that we will slip up from time to time (not purposely). That will not make us sinners BECAUSE we have been saved and BECAUSE we make a practice of being Christ-like, not a practice of sinning. I believe that if you make a HABIT of sinning with no kind of remorse then yes you are a sinner. That's just pure disrespect. And if you became a christian yet your lifestyle has never been any different compared to when you weren't saved, then I think that's more fitting of a "christian" being a sinner.
Sorry this post is so long. I wanted to say something the other day but couldn't put it clearly. But tonight I was reading 1 John 3:1-10(Life Application Bible), and it made everything perfectly clear for me. I think like someone else said that when most christians call themselves a sinner, it's semantics. Therefore, I hope these verses clears that up. Someone else please chime in. I hope I conveyed my take on it. Thanks for reading. (As you can see I don't post much, lol)