If you're a real-life human person with even a vague sense of humor, then you know that embarrassing your siblings is the ultimate pastime.
I mean, we have to put up with their garbage until the end of time, so why not have some fun messing with them? That's especially effective if you have younger siblings who stole the limelight from your perfection who now obviously need passive-aggressive takedowns. You know, to put them in their place.
And what this girl's sister does every day when she drops her off for school is pure sibling rivalry genius. When they pull up out front, big sis horrifies little sis by bumping to some seriously ridiculous songs with the windows down and speakers blaring.