I believe that this insult goes back to the 12th century at least (1066 and all that).
The story goes, that when English archers were captured by the enemy (french), they would have the first and second fingers of their hand amputated so that they could no longer draw a longbow.
In battle, they would emphasise that they could still draw a longbow by prominently and antagonistically displaying their current ability to draw a longbow by prominently displaying said fingers in the infamous “V” sign, ie "We’ve still got our fingers you bastards!!!"
Back of hand towards the target = “eat me” etc
palm towards the target = “Victory!” “we’re all in this together, kid” etc.
Don’t know when the “Victory” sign was first observed, Winston “I personally won’t fight them on the beaches, you poor bastards will be doing that, not me” Churchill is the first one that I can recall.
Hope this helps.