Child of their parent’s double-first cousin with their other parent’s first cousin or are the child of their parent’s sesqui-first cousin with their other parent’s sesqui-first cousin.

Triple-3C:
Person who, in relation to the other person, has zero parents, zero grandparents, zero great-grandparents and six great-great-grandparents in common.

Two chicks who've slept with the same guy

To have roaches in your house basically

A cousin that shares a same pair of great great grandparents. Most people never met their third cousins. There’s plenty of people that never even met their second cousins.

3C:
1- Parent's second-cousin's child.
2- Grandparent's first-cousin's grandchild.
3- Great-grandparent's full sibling's great-grandchild.
4- Person who, in relation to the other person, has zero parents, zero grandparents, zero great-grandparents and two great-great-grandparents in common.

Great-grandparent's sibling's great-grandchild.