Teaching your granny to suck eggs

[warpig1]

What does this saying mean?

[chakka35]

Once upon a time many old people had no teeth at all because they'd all dropped out. An easy way of getting protein into your granny was to puncture each end of an egg and let her suck it. I presume that grannies became so good at this that to presume to teach them how to do it was insulting. Hence the modern use of the expression.

[warpig1]

Thanks chakka, thats what I thought but didn't want to use it in case I was wrong and looked like a total eejit!

[Quizmonster]

Click here for some historical background.