Why is the splashing sweat emoji associated with semen?

For obvious iconic reasons. It is the Emoji that looks the most like ejaculate. Even if it takes some imagination.

And food dye.

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What I find amusing, and of course semiotically inevitable, is how thoroughly this secondary meaning has become conventionalized. You’ll see the Emoji used to refer to ejaculate, without it being disambiguated through additional emoji. Such as, say, the eggplant.