As the one who submitted this terrifying creature (who probably has a name other than “Monty Python rabbit”, but that’s the name it has in my head so that’s what we’re going with), allow me to explain:
Both Saitama and the rabbit defeat their foes with a single violent attack, however Saitama always attacks second (giving his foe a chance to demonstrate their overwhelming strength, complete with widespread city attacks, several minor character shounen battle arcs and a long monologue) whereas the rabbit always attacks first (without mercy, without drama, without explanation, taking its foe completely by surprise). By the time it occurs to Saitama to punch this rabbit, he’s already dead. And it’s not as if this rabbit is rampaging across the city or recruiting an army of lesser villains or any of that stuff. No: the rabbit just sits there, minding its own business, until some dumbass shows up and invades its territory. Saitama is EXACTLY that dumbass.
Similar comedy rules apply to each character, in that they LOOK exceptionally weak and average up until they strike, however of the two: Saitama is notably larger and much further up in the food chain than a very ordinary-looking, unarmoured and unequipped rabbit. Also abuse to animals is not funny, whereas abuse BY animals? Extremely funny.
So, yes: in my opinion, the Monty Python rabbit would absolutely destroy Saitama, even as the latter turns to the camera to ask, “Who is this sassy lost pet?”.
That said, I do think there’s an argument for Genos being able to defeat the rabbit, on the basis that he actually pays attention to intel, knows better than to underestimate weak-looking opponents and is equipped with both range weapons and the comedy approach of using excessive force for situations that really don’t, at face value, appear to warrant it. Scissors (Saitama) might beat paper (Genos), but paper beats rock (killer rabbit).
