In _Tom Sawyer_, Chapter One, the new boy tells Tom: "You can lump
that hat if you don't like it. I dare you to knock it off -- and
anybody that'll take a dare will suck eggs." In the case of modern
usage of the word (especially on television), I naively hope that the
characters are talking about eggs, and I suspect that script writers
dance around the censors using that argument even though we all know
better. I have heard the expression "Don't teach your grandmother to
suck eggs," meaning, that you are being presumptuous in teaching an
older and more experienced person something that they already know.
In this case, sucking eggs refers to the removal of the yolk and
albumin from the egg by sucking (or blowing) it out of a small hole
in the end of the egg. Twain's use of the phrase "suck eggs" (or more
accurately, the new boy's use of the phrase) is meant to be an
insult. What I would like to know is this: what makes sucking eggs so
derogatory? I believe the expression "Don't teach your grandmother to
suck eggs" has its origins in Germany. That brings this issue close
to the question of translating humor. Was something lost in
translation? Just wondering.

John Evans