Blankety Blank

I’ve no one but myself to thank
for this prison cell so small and dank,
for when I went to rob that bank,
the truth is, if I’m being frank,
I was a doofus––a real wank.
In short, my planning really stank.
For when my gun I chanced to yank
to use against that man of rank
who challenged me as feckless crank,
my confident demeanor sank;
for I fear I drew a blank!

The prompt today was “Blank.”    https://dailypost.wordpress.com/prompts/blank/