At the end of the book, the whole Madman gang meets up with Karl at McDonald's during his cleanup shift. They get splashed by Tierden and Harris in one last mud puddle hit, then sit around for hours eating leftover burgers and talking about life. When Karl goes home, he finds Bill and his mother sitting on the couch together, the discussion about stealing Karl's money seeming to have taken place. Then, Karl goes to bed, curls up with Hairball, and tries to sleep. He thinks that maybe staying out late at Mickey D's was a bad idea—but he doesn't regret it.
The thing that stands out most about this ending is that for the first time in the whole book, things aren't nuts. Karl is at peace with his friends, his mom seems pretty chill, and Hairball is in no imminent danger of being traded in for Karl's virginity. Most importantly, there's a clear sense that life is going to go on in Karl's weird little universe. "So I was going to be tired tomorrow," he reflects. "So what? Once I got going, with so much to do and so much in front of me, I'd be up on my feet again, running like a crazy bastard" (27.52). With friends like his, we don't doubt it.