Pointing out the faults or errors of others can be difficult. When you do point them out, there is usually an awkward moment. But you can often soften the challenge with humor.
For example, my brother-in-law came into his house asking a friend, "Do you sleep in the middle of the bed?" Our friend was puzzled by the question. As he thought of an answer my brother-in-law said, "Well, you parked in the middle of the garage." We all laughed, including our friend who was told in a light manner, "You did not leave a place for me to park in my own garage when it was raining."
The point was made, and in the future our friend will leave room for the owner of the house to park in his own garage. Even if you can't find a way to verbalize a criticism with humor, just the mental exercise of exploring more tactful ways to express your criticism of the other person will soften your message.
William Congreve wrote, "Music hath charms to soothe a savage beast, to soften rocks, or bend a knotted oak." The same can be said of humor in communicating difficult messages.