Both "don't teach your
grandmother to
suck eggs" and "
teach your grandmother to suck
eggs" are in
common use, with the longer form meant to
dissuade the listener from trying to
instruct the speaker on some activity in which the speaker is more
accomplished. The shorter form is meant to advise the listener that his intended instruction to a
third party is, likewise, unnecessary. Both forms originate in a time when
false teeth were less common than they are now, and
raw or
soft-boiled eggs were a preferred form of
nourishment for many
older people.
A little something extra:
Teach your grandmother to suck eggs. Attempting to teach your elders and superiors. The French say, “The goslings want to drive the geese to pasture” (Les oisons veulent mener les ois paitre).
from Dictionary of Phrase and Fable; 1898; E. Cobham Brewer (1810–1897)