>>28549105It's weird so it's kind of taboo. It's a sensitive area and actually an erogenous zone and associated with smells. And if human beings produce sex pheromones the armpit should be rich with them, a major contributor. The armpit fold/"cleavage" is a warm fleshy place to stick your dick. It's a major natural source of body smell and taste. When arms are raised over the head the armpit will take on a variety of shapes depending on the musculature of the person. The resulting appearance is probably somehow instinctively reflective to some individuals of potential mate health. The smell and taste of someone's sweat reflects their diet and general health as well.
As an aside, maybe you've seen that gag where it shows a silhouette angle of some guy's armpit and it's made to look like a woman's stomach heading into her vaginal area and legs viewed from the side? I'm sure just keeping that much in mind about the general aesthetic of an armpit you can see why it might come to be associated with sexuality.
Also fetishes don't really need to be justified, that's kind of the point. But armpits (and feet) absolutely can be.
