The "Law of the North" is an amusing
convention -- used during large family/friend type gatherings --that helps settle seating issues. It states that if you leave your seat (for example to go to the
bathroom or get a glass of punch), that seat is now up for grabs. Anyone is now free to take that seat, regardless how recently the seat was vacated and how obviously temporary the previous sitter's absence is. If one protests you "took their seat" one invokes "Law of the North" in
defense.
For example,
Molly your
pregnant cousin gets up to go to the bathroom, yet again, and leaves the comfy recliner she was sitting on open. You come along, see no one sitting on the
recliner, and you sit down. Molly then returns...
Molly: Oh man, I was sitting there!
You: Sorry man, Law of the North!
While the Law of the North is seemingly harsh (especially when invoked in polite
familial company), it really does help ease matters regarding seat
etiquette. You're not constantly asking "was anyone just sitting here?"
The origin probably comes from the fact pioneering life in the North, like
Alaska or the Yukon, required harsh laws and people couldn't
stand on ceremony. They might have frozen to death.