Hi, all.
For truly “wrong” romantic/erotic parings, I tend to go towards dark humor. So, Dipper/Mabel isn’t quite a “wrong” pairing, though it raises the question that if they married in Kentucky and divorced in Arkansas, would they still be fraternal twins. I’m thinking more along the lines of Mr. Ed/receptive Wilbur, Granny/Mr. Drysdale, Uncle Joe/every female over the age of consent, etc.
Cheers!