Por que o Coringa sempre ri?

O Coringa sabe que Batman não o matará, e que o atual sistema de tribunais e prisões de Gotham é muito corrupto para que o Coringa seja julgado e preso adequadamente. Em O Cavaleiro das Trevas, o Coringa expressa isso:

You have nothing, nothing to threaten me with. Nothing to do with all your strength.

Batman nunca matará o Coringa, pois vai contra o que o Batman representa. Tanto o Coringa quanto o Batman sabem disso. O Coringa está rindo da frustração de Batman. Mesmo quando o Coringa está convencido de que ele realmente vai morrer, ele acredita que ganhou ao fazer o Batman quebrar sua única regra, que é não matar.

Resumo: o Coringa está rindo da frustração de Batman, desde que Gotham permaneça corrupto e o Batman mantenha sua moral, o Coringa sempre vencerá.

Esta citação do Coringa sugere que sua loucura é ainda maior quando ele está experimentando algo desagradável. Como sua loucura parece vir de encontrar piadas em lugares estranhos e rir incontrolavelmente, ele provavelmente começa a fazê-lo enquanto coisas desagradáveis ​​acontecem com ele.

Memories can be vile, repulsive little brutes. Like children I suppose. But can we live without them? Memories are what our reason is based upon. If we can’t face them, we deny reason itself! Although, why not? We aren’t contractually tied down to rationality! There is no sanity clause! So when you find yourself locked onto an unpleasant train of thought, heading for the places in your past where the screaming is unbearable, remember there’s always madness. Madness is the emergency exit… you can just step outside, and close the door on all those dreadful things that happened. You can lock them away… forever.”
_{Batman: The Killing Joke}

Mas então, o Coringa também diz isso sobre tentar entendê-lo

"The real joke is your stubborn, bone deep conviction that somehow, somewhere, all of this makes sense! That's what cracks me up each time!"
_{Batman #663}

Ele parece ter um prazer especial em atormentar o Batman, que ele vê tão louco quanto ele - mas do lado oposto da moeda.

“You are truly incorruptable aren’t you. You won’t kill me because of some misplaced sense of self-rightousness. And I won’t kill you because…you’re just too much fun. I get the feeling that you and I are destined to do this forever.”
_{The Dark Knight}

E se há algo em que o Coringa parece acreditar, é que alguém está "um dia ruim" longe da loucura. Ao olhar para tantas citações do Coringa, acredito que a piada de que ele está sempre rindo é o pequeno pedaço de loucura que ele vê em todo mundo. (Sua criação do Two-Face em algumas histórias também aponta para esse)

Gordon's been driven mad. I've proved my point. I've demonstrated there's no difference between me and everyone else! All it takes is one bad day to reduce the sanest man alive to lunacy. That's how far the world is from where I am. Just one bad day. You had a bad day once, am I right? I know I am. I can tell. You had a bad day and everything changed. Why else would you dress up as a flying rat? You had a bad day, and it drove you as crazy as everybody else... Only you won't admit it! You have to keep pretending that life makes sense, that there's some point to all this struggling! God you make me want to puke. I mean, what is it with you? What made you what you are? Girlfriend killed by the mob, maybe? Brother carved up by some mugger? Something like that, I bet.

I give you: the average man. Physically unremarkable, it instead possesses a deformed set of values. Notice the hideously bloated sense of humanity's importance. Also note the club-footed social conscience and the withered optimism. It's certainly not for the squeamish, is it? Most repulsive of all, are its frail and useless notions of order and sanity. If too much weight is placed upon them... they snap. How does it live, I hear you ask? How does this poor pathetic specimen survive in today's harsh and irrational environment? I'm afraid the sad answer is, "Not very well." Faced with the inescapable fact that human existence is mad, random, and pointless, one in eight of them crack up and go stark slavering buggo! Who can blame them? In a world as psychotic as this... any other response would be crazy!"
_{Batman: The Killing Joke}