The moment when Jean-Baptiste first hears laughter coming from the darkness of the water is big turning point. It’s what knocks him off the "bad faith wagon," so to speak. Of course, it’s not hard to put two and two together and realize that a woman jumped off the bridge and into the water, and it’s only by standing on a bridge hearing sounds from the water that Jean-Baptiste is reminded of it.
It soon becomes clear that this laughter is closely tied to the idea of judgment. (Look at this line: "Now my words have […] the purpose […] of silencing the laughter, of avoiding judgment personally.") Once you think of it this way, all the references to laughter make more sense. Jean-Baptiste hears the universe laughing at him because he feels the universe judging him. He laughs at his own speeches during his period of discovery because he’s judging himself to be a hypocrite. He still hears laughter "occasionally" while practicing the role of judge-penitent because he hasn’t completely escaped from judgment. If you want to convince yourself that laughter = judgment, go ahead and look through your text for some other instances of laughter.
The interesting question, then, is why laughter? Shouldn’t he hear screaming from the water? Or perhaps words like "Coward! Hypocrite!" hurled from the mouth of an accusatory judge. Again, this problem is nothing a few lines from the text can’t cure. First of all, "Slavery is preferable with a smile. […] I have always wanted to be served with a smile. If the maid looked sad, she poisoned my days." And secondly, "The laughter continued to drift my way, without my random efforts succeeding in divesting it of its benevolent, almost tender quality that hurt me." From here, there are a few different explanatory roads we can take to determine why laughter = judgment. The first is that this is Jean-Baptiste’s world, so he creates it as he sees fit. Remember that the purpose of his confession is to make you a slave to him, and at the same time to hand over his freedom to you and be free of this burden. Either way, according to him, there needs to be some smiling involved. Slavery, in his view, has to be masked with a smile – and so, perhaps, does the judgment he is trying to escape. He prefers to deal with judgment in the form of laughter, and so, in his world, judgment takes that more desirable form.
The other possibility is that this is classic absurdist stuff. There’s something nearly laughable about the permanent human condition of suffering in the world. It’s so horrible that it borders on the comic (just think Waiting for Godot and you’re good to go. While you’re at it, check out our Shmoop module for more on this awesome Beckett play). That’s why Jean-Baptiste describes the laughter as "benevolent, almost tender." That’s an absurdist’s way of describing the judgment that both imprisons and terrifies him.