Иcточник - рассылка c
www.fluent-english.ru. 
Dear correspondents:
I received this intriguing email from a fellow translator today.
Frankly, I think it's a bit far-fetched, and I have serious doubts about
its veracity. Indeed, I suspect that it may have been a recent
invention from America, where it is currently fashionable to invent
clever ways of reminding French people of their less-than-glorious
military past, especially against manly Anglo-Saxons. On the other
hand, who knows? At the very least, it's an intriguing and very
creative and intricate fabrication. Remember, I don't endorse this
story; I'm just passing it on for your own amusement. If any of you are
serious philologists or English historians and can actually confirm that
this is true, I'd be anxious to hear from you!
S.
-------------------------------------------
This is not meant to be crude. It is strictly for your edification and
enjoyment.
Before the Battle of Agincourt in 1415, the French, anticipating victory
over the English, proposed to cut off the middle finger of all captured
English soldiers. Without the middle finger, it would be impossible to
draw the renowned English longbow and therefore be incapable of fighting
in the future.
This famous weapon was made of the native English Yew tree, and the act
of drawing the longbow was known as "plucking the yew." Much to the
bewilderment of the French, the English won a major upset and began
mocking the French by waving their middle fingers at the defeated
French,saying, See, we can still "PLUCK YEW!"
Over the years, some 'folk etymologies' have grown up around this
symbolic gesture. Since 'pluck yew' is rather difficult to say (like
"pleasant mother pheasant plucker", which is who you had to go to for
the feathers used on the arrows for the longbow), the difficult
consonant cluster at the beginning has gradually changed to a
labiodental fricative 'F', and thus the words often used in conjunction
with the one-finger-salute are mistakenly thought to have something to
do with an intimate encounter. It is also because of the pheasant
feathers on the arrows that the symbolic gesture is known as "giving the
bird."
The Historical Origin of "The Finger"
Pluck yew! Мило! 
