Re: How I Met Your Mother: Barney and... (Spoilers ahead...)
They'd be Uncle Barney and Aunt Robin even if there's no relation, and if they don't end up together. Dunno if it's different in different parts of the country, but I've got a couple pairs of "aunts and uncles" that have no actual relation, just close family friends...
Perhaps, if I am very lucky, the feeble efforts of my lifetime will someday be noticed and maybe, in some small way, they will be acknowledged as the greatest works of genius ever created by man. ~Jack Handey