Very, very old joke made new

    Yesterday was my brother William's birthday, so last night we went out to the local restaurant we always visit, him, my dad, Margaret and me. My dad told a story. He said that when he was a child, a black man who had been in the Army, possibly during World War I, taught him a poem. Dad said he could never remember the last line. I don't mean never now, in his 90s, but never since the 1920s. He recited what he could remember, and I looked it up and found it on the Internet with the smart phone. It's not particularly safe for work, but my three actual readers are all more or less self-employed (or don't look me up from work). It went like this:
In days of old
When knights were bold
And paper wasn't invented
They wiped their ass
On blades of grass
And went away contented.
    Now he remembered the third line as "and men wore metal pants," so the poem the WWI vet told him was a different one. But he was happy with this one as a solution to the decades' old mystery. Here's one that gets in the metal pants, but leaves out the poop:
"In days of old, when men were bold, and pants were made of tin, no mortal cry escaped a guy who squatted on a pin."
    Maybe I'll try it out on Dad when I pick him up from dialysis.