Something that is both gay and incestual. The word is mostly used jokingly to describe something that is "worse" than incest.

Briefly, "the realization that each random passerby is living a life as vivid and complex as your own." Originally from the Dictionary of Obscure Sorrows, which has a lot more beautiful neologism definitions like this you might enjoy.

Origin assumed to be in Lativia. Gaycest is when to brothers are in a romantic relationship.