I don't believe in having a tough skin, or in developing one.
To the contrary, I believe that we need to develop sensitivity, gentleness, compassion, long-suffering, and to receive from Christ the peace that He has said that He has left us.
Peace I leave with you, my peace I give unto you: not as the world giveth, give I unto you. Let not your heart be troubled, neither let it be afraid. John 14:27
It is this very peace within which negates the need for a tough skin.
The long-suffering allows, as defined by the online dictionary: having or showing patience in spite of troubles, especially those caused by other people. We are told that patience when fully developed makes a perfect (whole, complete, mature, whole lacking nothing) person.
But let patience have her perfect work, that ye may be perfect and entire, wanting nothing. James 1:4
Now, those who are thought we might need a tough skin from are they very ones who need to develop that gentleness and compassion. For if any of those qualities were possessed for any other than their own, no one would have to have a thick skin. They, who are like this, I fear for their soul. (Matthew 18:6)
I also do not believe in love carefully concealed.
I believe in love being fully and openly and continually celebrated in one another, but not if it is tainted and poisoned from the activity of ridiculing and mistreatment of others, i.e. gloating... being the glue that holds a community together. We are called to be greater than this because we are greater than this, if it could only be known.
Only the insecure have to look down on others. If they could only know how much God loves them, other than intellectually, and how much God loves other people, no insecurity would play out with cliques and their inherent appearance of superiority causing others hurt and the thoughts of needing a thick skin.
I could probably go on... but I don't care for extremely long posts; therefore, in order to not be a hypocrite
I shall end here with:
For this reason I bow my knees to the Father of our Lord Jesus Christ, from whom the whole family in heaven and earth is named, that He would grant you, according to the riches of His glory, to be strengthened with might through His Spirit in the inner man, that Christ may dwell in your hearts through faith; that you, being rooted and grounded in love, may be able to comprehend with all the saints what is the width and length and depth and height— to know the love of Christ which passes knowledge; that you may be filled with all the fullness of God. Ephesians 3:14-19
Amen.