When someone at work tries to sound smart and says “ perception is reality” what is a good way to respond?

"That's what the last mass shooter thought too!"

vise versa is the truth

As you have percieved he is trying to be a smartarse.  at your  expense.

The most affective way  of bringing this idiot down ton earth in front of others, and deflating his ego is just to say "Bollocks", and then walk away, which leave him all alone with his own stupidity.

Works very well indeed.

You might say: 

“Oh! You are one of those”.

And leave it at that. 

It will probably peak his curiosity what are the “those”. But you try as far as possible not to answer any further.

If he presses you for an answer, just say: “You know, one of those.”

If he continue to press you further, just say: “If you do not know, perhaps you are better off not knowing in the first place.”

Just in case you need to know, “those” are people that still thinks the sun revolves around the earth because it is perceived to be rising and setting.

Right on man.  

“That’s a common misperception.”

"Those who choose not to live with reality will, most certainly, have reality come live with them." -- Skip Williamson.

The response could be "WRONG" “Perception is more important than reality."

---"If someone perceives something to be true, it is more important than if it is in fact true. This doesn't mean you should be duplicitous or deceitful, but don't go out of your way to correct a false assumption if it plays to your advantage.”

Your perception is your reality, why do you think the elite love to manipulate our perception of reality to favor them instead of the entire human race

Depends on the context.