Sibling Switch Squick

Let's say the main character's name is Alice. She has a brother named Bob. The creator writes a new series with a totally new character, also named Alice. Alice's love interest in the story just happens to be named Bob (or look exactly like him, or act like him), and even though they're new characters, it still causes a Squick reaction.

Compare and contrast Brother-Sister Incest and Twincest, which don't even bother with the Expy bit.

Examples of Sibling Switch Squick include:

Comic Books

Lana Lang and Superboy, based on one cover on Superdickery.com, were siblings in one story, when in almost every other, she's his love interest.
In the original Italian Martin Mystere comics, Diana was Martin's love interest, but in the French Martin Mystery cartoons she's his stepsister.

Literature

Stephen King's Desperation and The Regulators, depending on which you read first. Either way, the Carver family from one version of the story reverses who are siblings and who is married. In other words, David and Pie would be brother and sister in Desperation, and their parents Ellen and Ralph, but in The Regulators, they're married.

Live Action TV

Toward the end of Arrested Development, Tobias starts dating a woman(?) named Michael. He doesn't seem to mind that this is also the name of his brother-in-law.
- Also, early on in Arrested Development, Buster dated a woman named Lucille, although it became increasingly apparent that he was using her as a stand-in for his mother Lucille, since "Lucille 2" was his mother's age and a close friend of hers.

Buster: I'm leaving my mother for you. You're replacing my mother.

Variation in Scrubs. Dani dates a boy named Danny briefly, confusing other characters into thinking she shouts her own name during sex.
Inverted in Wizards of Waverly Place. Alex and Justin were originally going to be bickering best friends, before being made siblings with a whole lot of Relationship Writing Fumble.

Toys

In the original minicomics that came packaged with the Masters of the Universe action figures, the bird-man Stratos has a human wife named Delora. In one of the cartoons (the 80's one) Delora is the name of Stratos' bird-woman sister. The 2002 cartoon corrected this by naming Stratos' sister Hawke, after an one-shot bird-woman from the 80's series, thus taking the squick factor away.

Video Games

The relationship between Mega Man and Roll differs from series to series. She is treated like his younger sister in the original series, a protective older sister in Mega Man Legends, and a love interest in Battle Network.
- In the Battle Network series, Rock is his human Operator's dead twin brother. This relationship does not exist in the anime. The two are shipped. It is about as squicky as it sounds.
- If you read Roll's Diary at the end of Mega Man Legends 2, Roll admits that she's in love with Mega Man.

Webcomics

It's a bit disconcerting to start on Safe Havens because you're a Kevin and Kell fan and discover that the geneticist with big hair is in a relationship with the dyslexic sports star who always wears sunglasses. The two K&K characters by those descriptions are only step-siblings, but still.

Western Animation

In the comics Minnie Mouse has an Uncle Mortimer Mouse, but in the cartoons Mickey's rival for her affections is an obnoxious cretin also named Mortimer Mouse (he's called Montmorency Rodent in the comics). In Mickey's Once Upon a Christmas, Mortimer Mouse is the name of Minnie's boss. What's more confusing is that Walt originally wanted to name Mickey Mortimer, and that in the comics Mickey has a nephew named Morty, short for (what else?) Mortimer. No switching with siblings here...just everybody else.
In the original Marvel comics, Silver Samurai and Mariko Yashida were half-siblings. Their Wolverine and the X-Men versions are a married couple.