Why do these words sound so nasty?

“Cunnilingus. Or some ridiculous word like that.” “It is pretty ridiculous.” “But not as bad as fellatio.” “What’s wrong with that?” “It sounds all hoity-toity.” “Just think of it like this. Fella. She. Oh.” Her mouth forms the shape. Where did she learn that? In the church van on the way to a retreat? “Where did you learn that?” “I just made it up.” “Where have you been all my life?”