Basic Trope: Relatives are mistaken for a romantic couple.
- Straight: Bob brings his sister Alice to his house. His neighbor Charles asks Bob if she's his new girlfriend.
- Exaggerated:
- Several people make this mistake every time Alice and Bob are seen together in public.
- Alice and Bob are Half-Identical Twins. Nevertheless, everyone mistakes them for a romantic couple.
- Downplayed:
- Charles assumes that Alice and Bob are a couple, but says nothing.
- Alice and Bob are cousins.
- Justified:
- Charles didn't know that Bob had a sister; perhaps Alice lives in another city.
- Bob is a womanizer who often brings women home for sex.
- Alice and Bob, despite being siblings, do not look very similar.
- Inverted: Charles and his girlfriend Diane are mistaken for siblings, which is why Bob panics when he sees them kissing.
- Subverted:
- Charles reveals that he was joking, and knew all along that Alice was Bob's sister.
- While Alice is Bob's sister, she is his girlfriend too.
- Double Subverted:
- He was lying so Bob wouldn't hate him.
- Bob lives in Zoroastrian Persia, where Brother–Sister Incest was not only tolerated but encouraged. He wanted to make sure Charlie knew his relationship was "sacred" because he liked to brag about it.
- Parodied: Bob has a ridiculously large number of sisters, and every time one is introduced they're mistaken for his girlfriend.
- Zig Zagged: Charlie mistakes Alice and Bob for a couple, and they correct him. However, it turns out Alice and Bob are just messing with him and they aren't related after all. But then the story rolls around to revealing they're half-siblings or Kissing Cousins, much to their surprise. Except there's some ambiguity around the family tree, so there's a chance it's okay for them to date after all...
- Averted: Siblings are never mistaken for Love Interests.
- Enforced: "We need to give Charles another good joke. Let's have him mistake Bob's sister for a love interest."
- Lampshaded: "Wow, Bob! You've found yourself a hot girl." "That's my sister, dumbass. I told you I was bringing her over, didn't I?"
- Invoked: Bob wants an excuse to be mad at Charles, so he never mentions Alice, but eventually invites her over for dinner in the hope that Charles will make this mistake.
- Exploited: Alice pretends to be Bob's girlfriend without his knowledge because she wants to piss off Bob's ex.
- Defied: Bob shows Charles (and everyone else in his life) a photo of Alice to prevent this mistake from occurring.
- Discussed: "Wow, for blood siblings, Alice and Bob look nothing like each other. And they spend so much time together... I wonder if anyone's ever mistaken them for a couple."
- Conversed: "Why didn't Charles know about Alice? I thought he and Bob were friends."
- Played For Laughs: Bob freaks out hilariously every time this mistake is made.
- Played For Drama:
- Both Alice and Bob are offended by the Relative Error, and lose touch as a result.
- Bob's real girlfriend believes Bob to be cheating on her and breaks up with him without giving him a chance to explain himself.
- Alice was hoping to date Charles, but now that he thinks she's dating Bob she can't get him to go out with her, and he won't give her a chance to explain.
- Alice and Bob are siblings, but are Mistaken for Romance because they're more physically affectionate with each other than one would expect for siblings.
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