When did women enemies start having staring contests with sparks in the middle?
There are also a few instances of this for men rivals. I don't have the answer to your question, though.
Do you mean when the idiom sparkles & staring came up to signify enmity? No clue, but the staring part is pretty much visible all throughout nature when two opponents face each other who don't know about each other's true strength and try to decide the fight before it's over by waiting who will break off first and try to run. The sparks may just be a sign of electric / magnetic tension (physics major WAHa to the rescue plz) as a metaphor for psychological tension.
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There were some in Ranma 1/2 so it must be fairly old.
black background plus spark is one of those cliche boxing manga page fillers
that and the guitars
>Do you mean when the sparkles & staring idiom came up to signify enmity?
That's the one. I've seen plenty of staring, but it seems women do the sparks more often, usually when competing over a man and keeping a pleasant look on their faces.
...guitars?
Men compete with fists - sparks come afterwards