My girlfriend and I were having a conversation the other day about sexual euphemisms and I told her about the following I'd seen on Saturday Night Live's Weekend Update by Tina Fey
According to a report released Tuesday, female inmates in the United States have been victims of sexual misconduct by corrections employees in every state, except Minnesota. So ladies, if you wanna rob a bank, but you don't want your cooter poked, head to beautiful Minnesota, land of 10,000 lakes.
It can't be that old, Ben Jones on Dukes of Hazzard played a character named Cooter and nobody thought anything of it. I've heard it used in this context many times since I saw that.
I checked etymonline and it only talks about turtles and a vague reference to an obsolete use of the word coot. Clearly, that is not from where the connection came since its use as I've described is recent.
Best Answer
Connie Clare Eble, a professor of English at the University of North Carolina at Chapel Hill and scholar of slang, compiles annual examples of student slang words. The earliest entry for cooter, via Green's Dictionary of Slang, is from fall 1977.
From there, cooter or cooder meaning vagina is attested from 1986, probably via vulgar synecdoche. The Concise New Partridge Dictionary of Slang and Unconventional English also dates the use to 1986, probably from the same source.
Green's has a contemporaneous definition for coot from "Razorback Slang," an article by Gary Underwood appearing in the Spring/Summer 1975 issue of American Speech, based on slang terminology collected among University of Arkansas at Fayetteville undergraduates from 1970–72.
This is held to be an abbreviation of cooter, so this usage seems to have been in place among youth in the American South from at least the early 1970s.
Iva Cheung at the Strong Language blog covered the term in a 2015 post entitled "Cooters and Hooters," later republished in Slate. She points out a similarity with snapper or snapping turtle:
The ostensible purpose of the post was to point out the lack of relation between cooters and cooties, which should be noted. The post also points out (links in original)