CAMERON: (whispering to himself) I'm dying.
The phone rings, and Cameron answers. </em> FERRIS: <em>(over the phone)</em> You're not dying, you just can't think of anything good to do.
These two little words from Cameron do a good job of establishing his character very early in the film.
FERRIS: Pardon my French, but Cameron is so tight that if you stuck a lump of coal up his ass, in two weeks you'd have a diamond.
In other words, Cameron's one seriously anxious dude.
FERRIS: I'm serious, man. This is ridiculous, making me wait around the house for you.
CAMERON: Why can't you let me rot in peace?
FERRIS: Cameron, this is my ninth sick day. If I get caught, I don't graduate. I'm not doing it for me; I'm doing it for you.
CAMERON: Do you know what my diastolic is?
FERRIS: Be a man, take some Pepto-Bismol, get dressed and come on over here, I'm tired of this stuff.
CAMERON: Oh, shut up!
There are a few things to unpack here, Shmooper. First, all of Cameron's talk about rotting and his diastolic blood pressure reveals a lot about his mindset. He's fearful, he's making up excuses, and he talks like he's eighty years old, not eighteen.
Second, the fact that Cameron shouts an exasperated, "Oh, shut up!" suggests that he knows Ferris is right; he just doesn't want to hear it. Finally, it's definitely worth noting here that Ferris explicitly states that he's taking this day off for Cameron's sake, not his own. He knows his best friend's a basket case, and he wants to help before they graduate and go their separate ways.
SLOANE: What could happen to it? It's in a garage.
CAMERON: It could get wrecked, stolen, scratched, breathed on wrong... a pigeon could s*** on it! Who knows?
Just how toxic does Cameron think pigeon poop is? He's so afraid to take chances that he musters up a litany of excuses (some more legit than others) for why they shouldn't leave the car in the seemingly normal, well populated parking garage.
GARAGE ATTENDANT: You fellas have nothing to worry about. I'm a professional.
CAMERON: A professional what?
Cameron's skepticism is not only funny here, it's justified. As Cameron, Ferris, and Sloane will later learn, this parking garage attendant is not to be trusted.
FERRIS: I used to think that my family was the only one that had weirdness in it. That used to worry me. Then I saw how Cameron's family functioned. His home life is really twisted. That's why he's sick all the time. It really bothers him. He's the only guy I know who feels better when he's sick. If I had to live in that house, I'd probably pray for a disease, too. The place is like a museum. It's very beautiful and very cold, and you're not allowed to touch anything. Can you appreciate what it must've been like for Cameron to be in that joint as a baby? I'm actually amazed that I got the car out of the garage. I caught Cameron digging the ride once or twice. It's good for him. It teaches him to deal with his fear.
Dr. Bueller dives deep into Cameron's psyche and digs up some interesting, heartrending stuff that reveals a lot about why Cameron's such an insecure cat.
FERRIS: Cameron, what have you seen today?
CAMERON: Nothing good.
FERRIS: Nothing—wha—what do you mean "nothing good?" We've seen everything good. We've seen the whole city! We went to a museum; we saw priceless works of art! We ate—we ate pancreas!
Throughout the film, Cameron often seems determined to have a bad time, sometimes to an irritating degree. Why do you think that is? Does it give him pleasure to be brooding and disagreeable? Does he like the attention? Is he modeling his parents' behavior? And, more importantly, they ate pancreas? (They did, Shmooper. In a deleted scene.)
SLOANE: He didn't leave. He's probably doing something.
CAMERON: No, it really busts my hump, you know.
SLOANE: Aw, Cameron. He didn't ditch us or anything. He's here. He's here.
CAMERON: Hey, for all we know, he went back to school. Probably took the train home.
SLOANE: He would not go back to school.
CAMERON: Yeah, he'd do it; he'd just do it just to make me sweat.
SLOANE: No, he would not. Cameron, come on.
CAMERON: Makes me mad.
Cameron's starting to crack here. He's not just anxious, he's angry—heck, he's paranoid. As Sloane points out, there's no way Ferris went back to school. Still, Cameron thinks Ferris is out to get him. Living in his parents' cold culture of fear and order, he's conditioned to assume the worst in people, even his best friend since fifth grade.
CAMERON: You know, as long as I've known him, everything works for him. There's nothing he can't handle. I can't handle anything: school, parents, the future. Ferris can do anything.
We told you Cameron was starting to break. He wants what Ferris has. This is also the point in the film—after he discovers that Ferris didn't leave, but was sneaking on a parade float so he could dedicate "Danke Schoen" to his friend Cameron "who hasn't seen anything good today"—that Cameron finally relaxes. He and Sloane walk through the parade holding hands, discussing the future, and Cameron looks completely at ease. (Too bad it'll be so short-lived.)
CAMERON: You know, that whole time, I was just thinking things over. I was, like—I was, like, meditating. Then I sort of watched myself from inside. I realized it was ridiculous, being afraid, worrying about everything, wishing I was dead, all that s***. I'm tired of it. This is the best day of my life.
Did somebody say catharsis? All it took was a daytrip to Chicago, an emotional breakdown, and a dip in an unsuspecting stranger's backyard pool for Cameron to have an epiphany and realize it's time to stop being afraid.
CAMERON: Good. My father will come home; he'll see what I did. I can't hide this. He'll come home; he'll see what I did. He'll have to deal with me. I don't care. I really don't. I'm just tired of being afraid. Hell with him. I can't wait to see the look on the bastard's face.
Cameron is no longer filled with fear—he's filled with fight. Nobody puts Cameron in a corner anymore.