It's a quote from a book - part of the Percy Jackson and the Olympians series; the third one. (The Titan's Curse, I think it was called? *too lazy to check*) Anyway, there's a young girl character in the series who was turned into a tree, and another character in the series who's a total flirt, and the quote is him complaining to someone else about how pretty girls sometimes turn into trees. And. Yeah. It happens all the time in Greek mythology, rly. ...Well, maybe not quite that often, but still! There's a history of it, at least!