Fellow IRA cineaste member George Robinson (the author of the new critically acclaimed book "Essential Torah") pointed me to this story in The Scotsman. Apparently, William McGonagall has often been named the worst poet in the history of the world and now they've discovered a play he wrote called "Jack O' The Cudgel." It's bad too. One lecturer at Glasgow said, "Seldom has there been a writer of such indefatigable ambition, singularly unmatched by even a smidgen of talent. There's something a bit cruel about the repeated reprinting of McGonagall's work." Ouch.
McGonagall was also a terrible actor: he once played Macbeth but refused to leave the stage after his character was killed till the audience finally dragged him off. Another time his bad acting caused a riot until he was banned from trodding the boards. He famously once walked to Balmoral Castle to try to get Queen Victoria to name him poet laureate. He failed.
If this isn't the basis for a movie, I don't know what is. I see Billy Connolly in the lead. Here's a bit of his poetry, in case you thought they were exaggerating. From "The Tay Bridge Disaster" -- "Beautiful railway bridge of the Silv'ry Tay/ Alas! I am very sorry to say/ That ninety lives have been taken away/ On the last Sabbath day of 1879/ Which will be remembered for a very long time."