Convince me.

[Acephale]

Convince me
Convince me that I am not mad         Take away the word "that"
This padded cell is the home of artistry       Nothing wrong with this, but using nouns such as "padded cell" when speaking of madness is overdone. Take away "is"
And this straitjacket the uniform of creativity. 
Using the blood of the wicked as my paint   I try not to start with 'ing' words, because it seems to throw the poem off. I would start out with "I"
The bones of the crooked my brushes,
we will paint a mural of the duplex, 
the duplex that is my mind.  I would merge these "We will paint a mural of the duplex that is my mind," though I'm not sure what you mean by duplex. Duplicity sounds more appropriate. Since you already used the word 'paint' I'd suggest finding a synonym. You could say 'create' 'construct' whatever you like.  
the duplex that is my mind. 
For the shapeless and unhuman entities next door
tell me I am sane.

This is what it looks like with some of the suggested edits. 

Convince me I am not mad
This padded cell the home of artistry
and this straitjacket the uniform of creativity. 
I use the blood of the wicked as paint
The bones of the crooked my brush
to create a mural of my minds duplicity
For the shapeless and inhuman entities next door
tell me I am sane. 

You may want to ask yourself, who is this poem directed to? Is the cell supposed to be a metaphor for your mind, if so what is the straitjacket?