Back when I was in college, we used to play various tabletop RPGs a lot. For one of them (DragonQuest), the rules we had were fairly complex (game rules + house rules) and covered a lot of situations. The general rule of thumb was that, if you came up with something that the rules said was ok, even if a bit ridiculous; you could do it. The caveat being, it would be discussed post-session to see if it should work going forward. But everything flies once.
One night, one of the characters was transformed into a frog and knocked off a roof. He triggered a spell, Shadow Wings, which grants the play large wings made of shadow, allowing them to fly. However, the wings are large enough to lift a human... I imagine on the order of a 15-20' wingspan. The DM made it known that it was not reasonable for a frog to fly using them. Much debate happened because... everything flies once. At the end of the discussion, the frog was _not_ allowed to fly.
The result being a new quote came out of that night.
Everything flies once, except a frog.