"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.