Definitions include: rights to a sitting space recently vacated, that one intends on occupying again in the near future. One "calls fives" to claim, for example, a spot on a sofa when one gets up to use the bathroom. Anyone is permitted to sit in the seat during the person's absence, but must give it up immediately when that person returns. One would say, "I've got fives" while getting up from a seat.
Definitions include: A topic certain to provoke incendiary response and disunity from the community it is addressed to. Even if the majority of the community would enjoy discussing it in reasoned terms, it will reveal the single-issue wonks among them.