Look, all of us have friends that we don't necessarily think the best of. If you talk about how you truthfully feel about a person's behavior, how is that backstabbing? For all you know, he's said the same things to his friend openly.
Real friends will criticize you and praise you, false friends give you endless encouragement because "that's what friends do". It takes another level of intimacy as a friend to be able to receive criticism and give criticism to a friend.
"Well, then," the Cat went on, "you see a dog growls when it's angry, and wags its tail when it's pleased. Now I growl when I'm pleased, and wag my tail when I'm angry. Therefore I'm mad."