I think intelligent friends will be obliged to disillusion you. I'm going to call this one internet nonsense.
In the first place, that Agincourt story is normally told about the standard English TWO-finger gesture. The middle finger gesture is an American novelty. I don't actually believe it about the two-finger gesture either, because I'm sure it doesn't come from contemporary chronicles.
As for the word, dictionaries say it is "early 16th century: of Germanic origin (compare Swedish dialect focka and Dutch dialect fokkelen ); possibly from an Indo-European root meaning ‘strike’, shared by Latin pugnus ‘fist’."
In the first place, that Agincourt story is normally told about the standard English TWO-finger gesture. The middle finger gesture is an American novelty. I don't actually believe it about the two-finger gesture either, because I'm sure it doesn't come from contemporary chronicles.
As for the word, dictionaries say it is "early 16th century: of Germanic origin (compare Swedish dialect focka and Dutch dialect fokkelen ); possibly from an Indo-European root meaning ‘strike’, shared by Latin pugnus ‘fist’."