octuple-third-cousin
A person who has no parents, no grandparents, no great-grandparents, and a bunch of annoying great-great-grandparents in common with someone else.
My uncle’s cousin is an octuple-third-cousin. He’s related but still annoying.
They’re so related, but they don’t even know it. Like family trash.
That guy at the family reunion? Octuple-third-cousin. He came just to complain.