[Trigger warning: I'm not a fan of trigger warnings because they frequently patronize the audience, but if the idea of incest being taken lightly upsets you, please don't read further.]
For years, I've been searching for a verb that approximates the meaning of the highlighted portion of this sentence:
I want to have that last sandwich, unless you want it.
I also play a kind of logic game with myself, which I have called the "game of incest". The premise is that you imagine there are two people of whatever gender, and then randomly assign them multiple familial relations. Say, John and Jane are cousins, siblings and John is also Jane's grandfather. Then you backtrack and mentally construct a family tree that would permit these curious family ties.
It sounds sick, I know. Really it is a totally asexual exploitation of the definition of family members in the English language and America. An American, English-language solution could be totally invalid in a different culture.