We're all mad here.

Alice: But I don't want to go among mad people.
The Cat: Oh, you can't help that. We're all mad here. I'm mad. You're mad.
Alice:
How do you know I'm mad?
The Cat:
You must be. Or you wouldn't have come here.
Alice:
And how do you know that you're mad?
The Cat:
To begin with, a dog's not mad. You grant that?
Alice:
I suppose so.
The Cat:
Well, then, 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.

-- from Alice in Wonderland by Lewis Carroll