"I reject your
reality and substitute my own" is often said when someone is completely unwilling to accept the
truth and instead chooses to create their own version of reality. It's often used in a joking or sarcastic way to poke fun at people who are being stubborn or
delusional.
Person 1:
Dude, you failed the test. You need to study more next time.
Person 2: I reject your reality and substitute my own. I actually aced the test, but the
teacher accidentally marked my answers wrong.
Person 1: Uh, yeah
right. Keep telling yourself that.