"Sand in your vagina" is a phrase intended to convey a perception of extreme irritation, irrational moodiness, and a generally uptight attitude in the recipient. It is a slightly more vulgar way to express similar sentiments to having your "panties in a bunch" or a "stick up your ass," with all the added connotations of the millenia of fear, disgust, curiosity, and confusion associated with female genitalia. It is often delivered in the imperative form ("Wipe the sand out of your vagina!"), or as a condescending query in an infantile tone ("Aww, what's the matter? Do you have sand in your 'giny?").
The origins of this phrase are pretty obvious. Any woman can tell you that getting sand 'twixt your nethers is one of life's more uncomfortable experiences. Mucous membranes are delicate and sensitive. The closest comparison I can come up with is getting sand in your mouth and nose, but that analogy fails to fully capture the annoyance of vaginal sand invasion. Swimming in a natural body of water can result in a maddeningly thorough sand distribution that laughs at your futile attempts to cover your delicate bits with a bathing suit. The real frustration comes when you try to remedy the situation in the semi-public showers of the bathhouse at the beach. This procedure requires swallowing any sense of decorum and contorting yourself into positions under the showerhead that could, in a different context, qualify you for a job with Cirque du Soleil.
On a more serious note, sand is one of the leading causes of irritant vaginitis in prepubescent girls. The itchy presence of grains of sand leads to scratching, which leads to further sensitivity and irritation, which leads to more scratching and on occasion, bacterial infection. Young girls should be washed thoroughly after playing in sandboxes or at the beach. Just don't give them a bubble bath, which is the other leading cause of irritant vaginitis.
When I was a little girl, "sand in your vagina" was right up there with "dingleberry" and "turdburglar" on the list of phrases that would draw instantaneous maternal ire. In hushed tones, my siblings and I would taunt each other with these words of power when we were not quite safely out of earshot of parental units. Like many of the taboos of my childhood, it eventually became a running gag on South Park, specifically in the infamous episode "It Hits the Fan," which also featured 161 gratuitous usages of the word "shit."
I've recently discovered that this phrase only achieves its full dramatic impact when uttered without a hint of sarcasm by a fresh-faced Georgia peach while recounting the tale of a late-night skinny dipping expedition: "Ah had sah-and in mah vah-gin-ah!" You have to hear it to believe it.
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