I hate the ridiculously wide-spread belief that it’s based on a playboy bunny (a Nintendo character based on a sex magazine, really??), can I just leave two far more likely inspirations for it’s origin here, since I haven’t came across a single official source that this pokemon was based on a playboy bunny? Here we go;

I know these two pokemon aren’t from the same generation, but there’s a striking similarity between Lopunny and Diggersby. Both are rabbits and both have natural colouration. You know what they remind me of, if placed side by side? The classic ‘fat husband / beautiful wife’ sitcom trope. It’s a million times more likely that this is where at least some inspiration for these two pokemon came from, because both have a design that could make them a related species, and they are also both in the Field egg group (with Lopunny also being in the Human-Like group). There was also some pretty solid proof that at least some pokemon designs may be planned in advance, and if that's true it wouldn't be surprising that at least a concept of Diggersby already existed when Lopunny was released.

The other theory isn’t mine, I’ve found it in serebii forums, but it also seems more likely, especially as we’re talking about Japan; Lopunny is simply based on Sailor Moon. Sailor Moon’s name is Usagi, which means rabbit. What is Usagi well know for? For being hella clumsy - I haven’t ever watched the show and even I know that. What is Lopunny’s Ability called? Klutz.