Urethra murdering Amazonian fish.
Everyone knows the story, not everyone knows the specifics. The Candiru catfish lives in South America, is less than an inch long, is sneakily translucent, and spends its days swimming up penises, then attaching by expanding it’s spines and feasting on a healthy blood supply. The only way to remove it is by surgery, and yes, you can die from it. So if your boyfriend pisses you off on your South American vacation, suggest a skinny dip, but just make sure you seal your vagina with duct tape first (it’s really no worse than a bikini wax, right?).