Working with a client on his "superior idea" and suddenly this happens: (longer rant)

tl;dr;
Client wanted me to move a div by 3 millimetres to the left and blamed me for not being capable of doing so while giving him a nonsense about different resolutions and screen sizes. (Use a ruler, DUH)

Me: Here's the updated design layout as our designer specified.
Him: Looks good but it needs to be moved 3 millimetres to the left
Me: *Confused as hell* - Wait, did you just said 3 millimetres?
Him: Yes, is that a problem for you?
Me: *Amazed* Well, yes, you see, we don't measure in millimetres. We use pixels.
Him: Ahh, can't you do anything right!? Why do I have to deal with your nonsense of telling me that this is not impossible? Just take your god damn ruler and put it on your screen, then move it 3 millimetres to the left.
Me: You do realise that every person has a different size/resolution monitor so it won't work?
Him: I don't care. Just do your god damn job or i'll find someone else to do it.
*
Story continued in such manner - we spent an hour on skype moving the stupid <div> around until it hit his 3 millimetres mark.
*
His: See, you could do it.
Me: *Sends him screenshot of my own screen (his was 1024x768, mine 1920x1080) where page is broken and not aligned*
Him: Oh come on, you break every god damn thing. You are the worst. I'm going to find a better one. *hangs skype call*
Him: *3 days later* Hi, so, umm, I've talked to other developers and they said it's impossible to measure in millimetres. Can you revert those changes we did?

After all this I've fully realised that this person is sits at computer very rarely and does not how it even works...

when you gotta go, you gotta go