Above: The eyes of an educator.
Hold on a minute there:
Let's get the obvious out of the way: this is his goddamned job. He is the Dean of Students, not the Dean of Not Giving A Damn. People are always all up the public schools system's digestive tract for not taking a more active interest in their students and that's exactly what Mr. Rooney was doing. It doesn't matter if, on a personal level, he's a dick or not -- he is literally paid with your tax money to make sure kids aren't doing exactly what Ferris did. The kid can go to a museum and drive a sports car on the weekend. During the week, he and the other kids are Rooney's responsibility so they can, you know, get an education.
The movie glosses over the fact that Ferris couldn't read
And you know what? He was right all along. Ferris was skipping school. Worse yet, he lied to his parents and friends about being sick and pretty much got the whole town involved in the farce. He lied, he stole, and he caused millions in property damage by destroying Cameron's dad's beautiful car. That's not adorable, that's just being an egocentric cock. It wouldn't have been a satisfying movie ending to see Rooney expose Bueller for his douchebaggery, but it would have been by far the more just outcome. What happens instead is that Rooney loses his wallet and almost has his nipples ripped off by a Rottweiler.