The reality is a computation matrix, Keanu.

Wrong reference, you lose. Although one word is very, very close...

I know it was a Doctor Who reference from the Tom Baker episode, "The Deadly Assassin". Or at least, it could be - guess there could be multiple sources for your quote. Google searches show that your quote is continued into my quote.

I just threw in Keanu like an extra spice, riffing from the use of the word "matrix".

Or were you going for ...

The Dungeonmaster (1984 film)

Mestema: "In a future reality I shall destroy you!"
Paul Bradford: "I reject your reality and I substitute my own!"

which was later quoted by Adam Savage from Mythbusters ...

Definitely the Tom Baker quote.

I didn't know the source of the Adam quote.

And I lose.

Jeeeez, you guys are geeks.

And not all that good at it, either.

*runs away crying*

I reject your insult and substitute my own.