Teaching grandmother to suck eggs
Teaching grandmother to suck eggs is an English language saying meaning that a person is giving advice to someone else about a subject about which they already know (and probably more than the first person). "Egg sucking" removed the egg contents while preserving the shell intact. Two small holes were made on the ends of the egg, and the contents sucked out. The shell could then be painted or otherwise used for decorative purposes without it becoming rotten and smelling bad.
Origins of the phrase
"You would have me teach my Grandame to suck Eggs"
“I remember my old schoolmaster, who was a prodigious great scholar, used often to say, Polly matete cry town is my daskalon. The English of which, he told us, was, That a child may sometimes teach his grandmother to suck eggs”
“But what am I about? If my grandmother sucks eggs, was it I who taught her?”
"You see, Grandmama, before you extract the contents of this bird's egg by suction, you must make an incision at one extremity, and a corresponding orifice at the other." Grandmama's response is to the effect, "Dearie me! And we used to just make a hole at each end."
- In "Hog on Ice" (Harper & Row, New York, 1948), Charles Earle Funk says:
"To teach one's grandmother to suck eggs – To offer needless assistance; to waste one's efforts upon futile matters; especially, to offer advice to an expert. This particular expression is well over two hundred years old; it is just a variation of an older theme that was absurd enough to appeal to the popular fancy."
"... she was a sensible girl who didn’t talk very much or try to teach her grandmother to suck eggs.”
"Go teach your grandmother to suck eggs! I've been handling guns like this, flintlock and caplock, since before you were born."
- The line was also used (as a reference to Burl Ives' character in The Big Country) in the sixth episode of the first season of The Ren & Stimpy Show:
"I don't think you're happy enough! That's right! I'll teach you to be happy! I'll teach your grandmother to suck eggs! Now, boys and girls, let's try it again!"
- The phrase has been paraphrased by the character Minsc in the role-playing video game Baldur's Gate. Referring to his genius "Miniature giant space hamster" Boo, he says:
"Don't teach my hamster to suck eggs!"
- Egg sucking is the subject of this parody of a military instruction: How to Suck an Egg
"The purpose of this exercise is to follow precise unnecessary directions issued by a higher HQ. You have been directed to be in possession of a fresh empty eggshell for no apparent reason. Simple issuance of tasks being insufficient in any anal-retentive, career-oriented, hopelessly bureaucratic military staff society, the staff of the higher HQ have issued the following instructions."
"But suddenly Gollum remembered thieving from nests long ago, and sitting under the river bank teaching his grandmother, teaching his grandmother to suck — ‘Eggses!’ he hissed."
The use of the phrase "Suck-egg" for "a silly person" dates back to 1609, in the OED.