Cat: You're right. We're nuts. This is an insane conversation.
Lister: She'll never leave Fred and we know it.
Perverse Sexual Lust is a term for a real person's attraction to a fictional character.
It originated in a reader poll during the early days of the webcomic It's Walky!. The author wished to know the reason behind the slightly loopy church-girl character Joyce Brown's popularity, and saw this option achieve an overwhelming win.
It's somewhat justifiable in live action, especially if the character is played by a hot person, although it does raise the question of what is actually being fancied. Is a viewer fancying CSI NY's Lindsay Monroe because of Anna Belknap, the character herself, or a combination of the two?.
It gets into the seriously weird when you're dealing with animated characters, although putting purely fictional characters into ahem situations has less creepy spillover to any real life people. Let's face it, a lot of Shipping would actually be wrong if we applied the same standards to Real Life. And, of course, many animated characters are intended to be attractive to the viewer, in which case it could be argued that this is the response the character designers intended in the first place.
As with many things, Japan has a specific term for Perverse Sexual Lust: "Nijigen no fechi" (二次元のフェチ)—literally, "two-dimensional fetish". More than a few otaku suffer from this syndrome, developing crushes on popular anime, manga, and even videogame characters, in some cases to the point where they prefer the objects of their crushes to "real" girls/women. In fact, according to these news articles, some fans even go so far as to attempt to marry the objects of their desire.
No examples, please; this is here to define the trope.