At a major gig at the Edinburgh Festival, he needed alcohol, lots of it, to ease him into the persona of Johnny Vegas, the drunken, ranting, sharp-as-a-knife comedian who the audience had paid to see.
But short of money and low on booze, Pennington found himself uncharacteristically sober. "I had to drink to get Johnny up to ranting pace," he explains.
As Eddie Izzard welcomed him on stage, his fate was sealed. Without alcohol, he was simply Michael Pennington, a quiet, gently witty guy with none of the unrelenting bravado of his acerbic alter ego.
Several minutes of excruciating silence followed as he willed Johnny Vegas to emerge but he was a no-show and the act fell horrendously flat.
It's just one of the anecdotes penned by Pennington in his autobiography, Becoming Johnny Vegas, in which he tries to analyse how and why Vegas came to be, and how he obliterated Michael Pennington completely.
It's a worrying tale written by someone who was apparently living a schizophrenic existence - he writes about Johnny in the third person, as though it was 'he' who was taking over and becoming the monster who ensured that Pennington ceased to exist.
Today, appearing much more sober and having lost a few stone in weight since his stand-up days, he explains: "I wanted to try and trace the genuine origins of Johnny and how he so successfully staged this takeover of Michael Pennington."
The 42-year-old comedian, actor and director, who originally trained as a potter in Glasgow, continues: "Johnny is a contradiction to who I am as a person. I'm not very good at confrontation, I have a tendency to internalise and to carry things around.
"Johnny was a coping mechanism, getting laughs from things that would have otherwise upset me."
Brought up in a strict Roman Catholic household, some of the blame for Johnny's emergence may be laid at the door of the cold, unloving seminary in Lancashire which the young Michael attended as a trainee Catholic priest when he was aged just 11.
"I came from a very loving home, had a happy life, with no great aspirations, but going to the seminary changed me. There was a chunk of my childhood missing," he says.
"Once I'd realised I'd made a mistake and it wasn't for me, I still felt this tremendous pressure to continue with it, for fear of letting everybody down."
He lasted 18 months, but when he returned home to St Helens to attend regular secondary school, he didn't fit in.
"I felt like a 30-year-old trapped in the body of a 13-year-old."
When bullies threatened him, he retorted by saying he'd pray for them and it was then that the first signs of Johnny appeared, giving him the back-up he needed to survive.
Pennington also suffered from hypochondria, thinking he had every ailment from lockjaw to cancer, but brave Johnny Vegas killed those fears. "What would stop it was alcohol and that would encourage Johnny out, but you can't stay drunk the whole time."
He still doesn't know how much Guinness and vodka he drank during his stand-up days in pubs and clubs, or when he was nominated for the Edinburgh Festival's Perrier Award in 1997, or on sell-out tours.
It was the birth of his son, Michael Jr (who is now 10), from his first marriage to Kitty Donnelly, which made Michael Pennington take control again.
"It took me back to a time when I was really happy and I thought, 'My son doesn't deserve Johnny Vegas as a dad'.. It was the start of a hard battle."
Public expectations made ridding himself of the demon of Johnny Vegas harder, he reflects, as he tried to build a career which didn't involve getting drunk.
He was lucky that other things came into place, including acting roles in the BBC series Bleak House and the sitcoms Benidorm and Ideal.
"I'd love to play a really good baddie," he adds.
He has directed various one-off TV and radio dramas, has just completed series three of Moone Boy and recently directed and co-wrote Ragged, a one-off drama starring Ricky Tomlinson for Sky Arts.
He feels happy behind the camera, saying: "It's more of a job for Michael Pennington."
Remarried in 2011 to Irish TV producer Maia Dunphy, Pennington credits her with helping him keep the lid on Johnny Vegas.
"My wife has made a huge difference. I don't feel like I'm searching for things any more.
"Johnny would get easily distracted by friends who'd say, 'We'll just go for one drink', and it would turn into five.
"Now that doesn't happen. I have a good social life with friends, but most weekends I've got my son."
So will Johnny Vegas ever emerge again?
"There are certain panel shows where I need to borrow a watered-down version of Johnny from time to time, so I can let him out of the bottle and get him back in straight away. He's not allowed to bleed out into my lifestyle."
l Becoming Johnny Vegas by Johnny Vegas (£20, HarperCollins)