As best as I can tell, Virginia law prohibits many (though not all) incestuous marriages with gender-specific nouns only (§ 20-38.1):
(a) The following marriages are prohibited:
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(2) A marriage between an ancestor and descendant, or between a brother and a sister, whether the relationship is by the half or the whole blood or by adoption;
(3) A marriage between an uncle and a niece or between an aunt and a nephew, whether the relationship is by the half or the whole blood.
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And it prohibits sexual relations only between people for whom the law forbids marriage (§ 18.2-366):
A. Any person who commits adultery or fornication with any person whom he or she is forbidden by law to marry shall be guilty of a Class 1 misdemeanor except as provided by subsection B.
B. Any person who commits adultery or fornication with his daughter or granddaughter, or with her son or grandson, or her father or his mother, shall be guilty of a Class 5 felony. However, if a parent or grandparent commits adultery or fornication with his or her child or grandchild, and such child or grandchild is at least thirteen years of age but less than eighteen years of age at the time of the offense, such parent or grandparent shall be guilty of a Class 3 felony.
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Except certain types of acts, which are explicitly forbidden with specific relatives (§ 18.2-361):
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B. Any person who performs or causes to be performed cunnilingus, fellatio, anilingus, or anal intercourse upon or by his daughter or granddaughter, son or grandson, brother or sister, or father or mother is guilty of a Class 5 felony. However, if a parent or grandparent commits any such act with his child or grandchild and such child or grandchild is at least 13 but less than 18 years of age at the time of the offense, such parent or grandparent is guilty of a Class 3 felony.
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Same-sex marriages were forbidden in another section of the Virginia Code, but the U.S. Supreme Court has held that states cannot prohibit same-sex marriages.
In light of that ruling, does that mean the lines of the classic South Park song (Warning: explicit) would not constitute incest in Virginia?