On a blog thread the other day I recounted that on my first day in a new parish, a second curacy, one of the churchwardens, very much the senior one, was about to introduce me to his wife after Evensong. I had met the lady earlier that day at the 8am Holy Communion. I therefore interrupted the churchwarden to say 'Oh I've already met your MOTHER.'
What made it more inexcusable was that she wasn't even older than him. Fortunately she was one of those Christians who really did forgive. As far as I know she never held it against me.
In my defence (or is it hers?) I can without effort be twenty years out on either side in guessing any person's age.