An infamous feature of the equally infamous Fantasy Adventure to Adult Lechery (or From Another Time Another Land) role-playing game, the Anal Circumference table enabled players to determine the maximum size of object their character's anus could accommodate without tearing, because this was an important part of characters due to the prevalence of rape in the game. The meme is most commonly deployed on /tg/ in the form "ROLL FOR ANAL CIRCUMFERENCE" as a response to some sort of impending disaster, the implication being that you are about to be literally or metaphorically arse-raped so hard that you better check to see whether or not your body can take it without tearing.
Like most aspects of FATAL, this is bizarre and terrible not only in concept but in execution, as the numbers the table provides make little sense. What we DO know however is that elderly people have a tighter anus than middle aged ones, since they get a smaller modifier to their roll. Also, it's entirely possible for someone to be accustomed to anal sex and yet unable to take a dick in their arse. The eagle-eyed will observe that the table shown below has a modifier for infants, just in case you were mixing and matching your sexual deviancies and are curious as to exactly how much your /d/elightful player character is destroying a small child's anus (as it happens, that row was removed in the second version of FATAL's rulebook). Fortunately, one in forty human infants have an anal circumference of 4-5 inches. Goatse-man approves.
Earlier editions made it possible to have zero or even NEGATIVE anal circumference, which can help you in ways you can only imagine since this effectively means you have no anus. If you don't understand why this is good, it must be your first time playing FATAL and your GM will show you why soon enough. The only downside is that you can't take a shit, but if you're playing FATAL you already couldn't give one.