Casual friends want to distinguish themselves from enemies, and they might use signals of warmth and friendliness—things like smiles, hugs, and remembering small details about each other. Meanwhile, close friends want to distinguish themselves from casual friends, and one of the ways they can do it is by being unfriendly, at least on the surface. When a close friend forgets his wallet and can’t pay for lunch, you might call him an idiot. This works only when you’re so confident of your friendship that you can (playfully) insult him, without worrying that it will jeopardize your friendship.
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