Has an AFL game ever ended 121-31?
Exactly once. On August 21, 1915, Fitzroy beat Geelong 121-31, and no AFL game before or since has ended that way. When it happened it was a scorigami, the first 121-31 in league history.
That makes 121-31 the 3836th most common final score out of 6,607 that have ever occurred in AFL. One point away, 122-31 has happened 1 times and 121-32 has happened never.