John is the most common male human name in the English-speaking world for centuries, and giving it to a pet is the ultimate act of deliberate anticlimactic naming. The gap between the name's radical ordinariness and the animal's inherent cuteness is so wide it loops back around to being interesting.
The Maximum Ordinary Effect
Naming a pet John is a more extreme version of naming it Joe or Tom — those are already plain, but John is the plainest. There's no pop-culture reference, no vintage charm, no irony available. It's just the most common name. That blankness is either a feature or a bug depending on your philosophy. A golden retriever named John has a deflationary effect that some owners find genuinely amusing.
Historical Weight
John comes from Hebrew Yochanan, meaning "God is gracious," and has been borne by more saints, kings, presidents, and popes than almost any other name. The human name John is the anglicized form of Iohannes, which spread through early Christian naming. For a pet, none of that history is legible — it just reads as flat and a little funny.
An Honest Note
If you're naming a pet John and you're not doing it as a deliberate bit, consider whether the name will hold its appeal over fifteen years. Joke names work best when the owner commits fully. For something just as simple but with more personality, Joe and Tom have more charm. Browse all pet names for alternatives.