About a year, in fact.
So he knew his next play had to deal with subject matter which was perhaps a little lighter, a little less demanding.
"Yes, it was tricky trying to work out how to kill a baby in a play – especially when the play is a comedy," says the Glasgow-based writer.
He's talking about the play he's writing for the Abbey Theatre in Dublin.
"I had spent about a year working on the story, based on this idea that a grandfather looks at his daughter for the first time and all he can see is the face of Gerry Adams.
"So I reckoned the next play should be less dark."
The playwright, a Belfast-born former actor who trained at Glasgow's RSAMD and had his first play performed at Oran Mor, loves to explore the darkness.
But overall he writes great comedies that take a scalpel to the human condition.
Previous Oran Mor plays have resulted in almost riotous laughter.
The End of Hope, The End of Desire, for example, featured a poet and a prostitute in bed, with the prostitute wearing a mouse's head for the first 15 minutes.
The story was essentially about the masks people wear in their lives. And this dark believability, a recognition of truth, proved the springboard for huge audience laughs.
David's new play again explores relationship territory, again with a twist.
Most Favoured is the story of a couple who wake up in a hotel in Edinburgh, where they have been attending the Fringe.
But the couple don't know each other. They've had one-night stand. And there's a culture clash.
She's from Glasgow, and he's American.
"She found the experience from the night before very strange," explains David.
"And so she has to talk to him about the night before."
Is the play autobiographical?
"Not in the least," he says, smiling.
"I usually have no idea where the ideas come from.
"For example, the idea of a baby looking like Gerry Adams came out of nowhere, in fact when I was having a conversation with a theatre boss about something else.
"And this idea for Most Favoured? Who knows?"
David, who met his wife Jennifer at Oran Mor, is a huge fan of writers such as Neil Simon and Woody Allen,
"Perhaps I had been reading a Neil Simon play when I came up with this," he says.
"But I like it. It has a Neil Simon vibe about it.
AND the interesting thing is it's the first play I have written in which the characters don't come from Belfast.
"It's strange to hear my own voice coming through the Glasgow and American accents. But I was keen to write a Glasgow voice.
"And I wrote it with Gabe Quigley (who stars alongside Jordan McCurrach in the play) in mind."
Most Favoured "goes to some strange places" which, the writer won't reveal in fear of spoiling the plot.
But of course it wouldn't be a David Ireland play if it chose to stick to the path most trodden.
"I guess that's right," he says.
"Sometimes I do get a little dark."
There seems little doubt he will be able to capture the essence of a Glasgow character, and indeed an American.
David agrees with the notion it often takes an outsider to hold up the mirror, to reflect what's actually going on in the world in which those born locally take for granted.
"Yes, there is a good tradition of Irish writers such as Oscar Wilde or George Bernard Shaw writing so well about British society," he points out, before breaks into a laugh.
"Oh, no. I've already compared myself to Neil Simon, Oscar Wilde and George Bernard Shaw. What will people expect?"
If they have seen the previous David Ireland plays they will expect sore sides by end of lunchtime.
l Most Favoured, Oran Mor, until Saturday.