People's blindness makes no sense
When you watch this movie a few times, it starts to occur; many people have some kind of REALLY weird, selective blindness or visual impairment.
Jeannie doesn't recognize the principal, when it takes about 0.01 seconds to recognize someone you know? HOW can she not see the face of someone she KICKS IN THE FACE?! (Multiple times due to editing)
The 'dad' never sees Ferris, although he looks STRAIGHT at him several times in the movie. His eyes receive the photons that have been radiated from Ferris, but somehow he doesn't SEE him. This is not humanly possible, but we're supposed to accept it.
The mom doesn't see Ferris, who is RIGHT IN FRONT OF HER after Jeanie slams the brakes so they won't hit him. How can a passenger of a car not see WHY the driver hit the brakes so hard, and how can a passenger NOT BE CURIOUS as to what happened and why? No passenger in the world would just look at her papers and be angry at her WITHOUT CHECKING whether there's an actual REASON for such braking.
I mean, if the mom takes as granted that her daughter is THAT bad at driving that braking wildly for no reason is a COMMON OCCURRENCE, then it follows that she would keep an eye on her driving EVERY SINGLE SECOND SHE POSSIBLY CAN to not only evaluate her driving, see what causes to behave like that, but also to advice, help and guide her to become a better driver.
She cares about her daughter, right? What caring mom would NOT do the things I just mentioned for her beloved daughter?
In any case, people would be VERY alert if they're in a car that suddenly stops so violently. Everyone in the car would want to know what caused it, including a passenger in the front seat.
The dad's friends/associates/clients/workbuddies/whatever never see (or hear) the three wildly-moving kids right next to them, or react to them.
Absolutely NO ONE sees Ferris fake-sing on the parade float. How?
Somehow everyone knows Ferris, but somehow no one knows Ferris, when it's convenient. The garage 'car borrowers' don't report having seen Ferris being not-sick to anyone. The people watching the parade don't see and/or report him to anyone, although even the cops think Ferris is sick and thus can't be outside.
What's going on with people's vision(s) in this movie? Can anyone honestly tell me people would be this vision-impaired in real life if these situations happened for real? We ALL know in our hearts that the movie takes quite enormous leaps to abuse our suspense of disbelief violently, when it comes to people's vision, and in real life, Ferris would've been caught very quickly, in so many ways and scenes, it boggles the mind.
They could've at least made it a bit more realistic, as nothing is as annoying as 'convenient blindness that doesn't make any sense'.