Stylistic device:

Device of styles

Wordplay:

Play with words

Apparent oxymoron:

“Inveterate Vegetarian”

“Inveterate” is synonymous with “absolute” in the vernacular.

Someone who advocates or pursues a cause with conviction does so   

“inveterately.”

Thus, the absolute plant-eating meat lover is an inveterate plant eater.

Do you know? Do you understand?

Yes?  Good.

No? It’s just a play on words.