I’m gonna take this in good faith as an honest question, so forgive me if I am overthinking a joke. :)

But both animal and human tits are inherently vegan, they serve a biological purpose for feeding young. A baby drinking mothers milk is vegan because it’s both freely given and literally just basic biological nature for mammals. Likewise when a cow gives birth and then their milk is intended for their calves, that’s absolutely still vegan. But when an animal is harmed such as in death for meat or raped as in case of having the mother produce dairy, then it stops being nature and becomes non-vegan exploitation of a creature with no meaningful way to consent to or resist their own harm.

So my wifes tits are indeed vegan because she enthusiastically consents to people getting off to 'em!