First, realize that this friend may never accept advice. While they are encouraged by the Word, they may not adhere to God's correction from the Word. Time after time and over and over, they jab your side. It hurts. The thorn could eventually gauge your side, draw blood, and embed itself in your body. To heal, you must remove that thorn. But, before allowing it to embed itself, ask how Jesus would act.
I'm sure you can visualize many examples of thorn-like friends. I have an author friend who wrote a blog and her thorn-friend constantly copied her ideas, her blogs, and even her books. I empathize with her because I've experienced that also. It takes a lot of work to get those blogs or books written for readers and then to see it copied is unfair. Not to mention, it is plagiarism. So what did my friend do? My friend quit writing. Yes, she did. The situation seemed impossible to resolve, so she just gave up.
We must never give up on what calls us to do. We shouldn't be afraid but trust God to work a way around the thrones, through the thorns, or by the thorns. He will do it. "Faithful is He who calls you who will also do it." First Thessalonians 5:24 (NIV) Remember roses emerge through the thorns. Don't pluck out the rose bush because of the thorns. Look for the roses. Prune the thorns back so you can enjoy the roses. If the whole bush is just thorns, then remove it. It may be time.
How about you? Is it time to prune the thorns around you? Or, are you the thorn? I know in marriage, we sometimes don't recognize how we jab away at our relationship daily. If we don't realize our spouse's (or friend's) wounds, inflicted by us, we may wake up alone one day with no friends and maybe no marriage.
While we all have those thorns in close proximity, let's look for the roses, prune the thorns, and avoid the anguish of bad relationships.