Green’s Dictionary of Slang

a piece of excrement poking out of the anus, due to the urgent need to defecate.

1999		L. Gould Shagadelically Speaking 122: Where’s your shitter? I’ve gotta turtle head pokin’ out.
2000		T. Udo Vatican Bloodbath 60: She nursed a stubborn turtle’s head out of her partially dilated anus with her left index finger.
2004		P. Howard PS, I Scored the Bridesmaids 133: I’m actually wondering whether I’ve got constipation, it’s that long since the turtle showed his head.
2009		R. Milward Ten Storey Love Song 19: [B]ubbles in his colon and a sloppy turtlehead waking u from hibernation.
2015		J. Stahl OG Dad 79: The phrase turtlehead comes to mind, and I want to douse my brain with lighter fluid and strike a match as soon as I think of it.
2015		N. Cummins Tales of the Honey Badger [ebook] I was shit scared and had a turtle head poking out and headbutting me undies.