So I'm not anticipating much trouble with this week's mission. Deciding which of my grandmothers should be on the receiving end of this lesson is going to be the hard part. The first contender is Edie Sweet, 78, former Wren and priest's housekeeper, now in a wheelchair and living in a convent in Hull. The second contender is Marjorie Johnson, 82, retired comptometrix, pork crackling enthusiast, scourge of the Daily Express Trackword, and often favourably compared to Merle Oberon.
Since I can't really see the nuns approving this project, I think Marjorie is my best bet. And she has her own theory about the meaning of the expression.
"Older people haven't any teeth, and it was easy for them to go [makes sucking noise]. If you've got teeth in the way, that's much more difficult. You can't teach your grandmother to suck eggs because she already knows how to do it."
"So you're an expert at this, then?"
"No, I've never done it before."
"Well, neither have I."
"Yes, well. You're not a grandmother."
We're sitting in my parents' kitchen, either side of the big wooden table, a bit like John Malkovich and Matt Damon in Rounders. My mum supplies two wooden kebab skewers, two nails and two bendy straws. Then she brings on the egg-rack, the only useful thing I ever made in woodwork. Should Sir Terence Conran be reading this, I'll gladly sell the rights to reproduce them in citrus- coloured plastic.
"Choose your egg," I instruct.
"Does it matter which one?" she asks.
"Well, what do you look for in an egg?"
"That it's oval." And Gran selects one, completely failing to go into that standard old people's monologue about how they used to have lions stamped on them.
"Now start with the nail, and make a little hole in either end. Then stick the skewer into one of them to make it big enough to get the straw in."
But the first stage is causing some problems. "Maybe we need hammers," Gran wonders.
"We need an egg tooth, like a baby chicken," I suggest.
"We haven't got a baby chicken," reflects Gran. A moment later, I've managed to pierce my egg by turning the nail on the surface of the shell as if I was trying to set fire to it. Gran's still having trouble. "Can I let you start it, and then I can do the bit with the skewer?" she asks, so I give her the one I've just broken into. This is my big mistake. She takes the pre-pierced egg and as I'm trying to make holes in a second one, my Mum points out that you don't really need to get the straw inside the egg, as long as you cover the hole with it. So while I'm still plugging away with the nail, Gran just puts the straw on to the hole in the top of her egg, and begins to suck noisily. The white is rising up the straw, and I haven't even started yet. So you can't teach your grandmother to suck eggs: she'll pretend to be too feeble to get started, then race ahead to the finishing post. Still, after 82 years you've got to have learned something.