In Judy Blume's coming-of-age book "Forever", Ralph is what Katharine's boyfriend calls his penis.
The fevered young couple are in bed making out, and the dude actually introduces his penis, saying "I'd like you to meet Ralph". The virginal Katharine studies the situation a minute, and then narrates the line that will forever live in infamy... "Ralph was small and soft in my hand." Later, she describes Ralph pushing against her. It all seems a little bit schizophrenic and kinky, less like a first encounter and more like a ménage à trois.
Guys who name their penises... what can I say? Imagine introducing your breasts to someone: "How are you, Dick? I'm Tiffany! Meet Bobbie, here on the right, and over here in the left cup, Bunny!
And if you're going to name your dick, then "Ralph", which is slang for vomiting, seems an unwise choice.