I wonder if Peter called on people to speak of Christ "with gentleness and respect" because of the way Jesus himself dealt with those who were willing to learn. The Samaritan lady at the well could have been called unpleasant names -- probably had been called names at times. But Jesus treated her with gentleness and respect. Simon the Leper, the man who hosted the dinner where Jesus was anointed by a sinful woman, could have been criticized harshly when he tried to distance Jesus from the probably-uninvited guest, but Jesus dealt with him with gentleness and respect, setting up a story about two people who needed forgiveness, asking his opinion about it, giving him a chance to have the right answer to Jesus' question. When Jesus was criticized over having dinner at Levi's house, he turned that criticism into more than a teaching moment -- it was a faith-building moment as he took an opportunity to explain more about God's grace and our hope. (That was the occasion when he said, "It is not the healthy who need a doctor" etc., explaining more about the hope for the spiritually ill.)
I have recently been reading a Harry Potter fan-fiction* that is written to show what good parenting might have done for Harry, and it shows "constructive criticism" done in an interesting way. Whenever Harry does something fairly stupid, he is told that his new guardian will not accept foolishness from such a bright boy, and he expects better in the future. Whenever Harry does something risky, he is told that he is valuable and important, and is not to risk any harm coming to himself. As opposed to the Dursleys who raised Harry with harshness and hatred, here Harry is treated with gentleness and respect (comparatively speaking). Even well-deserved corrections are delivered with ... whatever you might call the opposite of "backhanded compliments" ... maybe "complimentary corrections"? At any rate, his value is presented as the reason for the correction when he falls short of this.
It seems like this is a skill that a Christian should want to master. Once a blog neighbor and I traded comments about a book called The Gentle Art of Verbal Self-Defense; while there is good in that book, at times the responses are not fully Christian, and the book is more defensive than constructive. There may be room in the world for a book about the The Gentle Art of Lifting Up Your Neighbor. I'm wondering whether to start a collection of the most apt turns of phrase for that purpose. If the readers have any suggestions for good books to read along those lines -- or good movies, as the case may be -- I'd be glad to hear about them.
* I can't fully recommend the fanfic as the author has something of a ... fetish ... to put it politely. You'll spot it quickly enough if you try to read it. But it's PG-13, and if you're interested the fic is here. Like almost everything, it has pro's and con's, and let the reader use discretion.