How can you disprove the statement $4=5$? I know this sounds insane. But bear with me, my friend said this to me with a straight face: 

Can you disprove the statement: $4=5$?

And I was like is that even a question, thats obvious, $5$ is $4+1$ and $5$ comes after $4$.
He was like: but you haven't still disproved my statement.
Something like this went for around 30 minutes...and he wasn't happy at the end at all
Is he correct? If not, how does one actually give a good sensible answer to such a person?

Hold up 4 fingers on your left hand. Hold up 5 fingers on your right hand (yes, count your thumb as a finger). Show that no matter how you try to pair them off, there's always one left over on your right hand. For added effect, make it the middle finger. 
