I keep changing my answers, lol. Actual incest is obvious, but when you get into familial-type relationships, where they're not actually related, I get indecisive, lol.
Sometimes that's really easy to determine - Buffy/Giles is obviously father/daughterish in nature. But others are more complicated, particularly pseudo-sibling relationships, since there's a fine line between "he's like a brother to me" and "he's a really good friend" (which could someday be more than that). Like, I can see Xander as a big brother to Dawn, but canonically she's had a crush on him, so clearly she hasn't always seen him as a big brother. On the other hand, Willow/Dawn and Tara/Dawn were both motherly relationships, actually living in the house and taking care of Dawn, so they squick me more.
no subject
Sometimes that's really easy to determine - Buffy/Giles is obviously father/daughterish in nature. But others are more complicated, particularly pseudo-sibling relationships, since there's a fine line between "he's like a brother to me" and "he's a really good friend" (which could someday be more than that). Like, I can see Xander as a big brother to Dawn, but canonically she's had a crush on him, so clearly she hasn't always seen him as a big brother. On the other hand, Willow/Dawn and Tara/Dawn were both motherly relationships, actually living in the house and taking care of Dawn, so they squick me more.