For a boy? It depends. To me, “Pup” implies a playful, gregarious nature, and a natural desire to find a place among men that have clearly outlined alpha and beta roles in a group. “Kitten” implies a more passive existence, perhaps that one of a spoiled, pampered sub or harem boy or houseboy. Someone that likes long naps and constant affection; someone skittish around crowded events and loud noises and prefers to be alone with their Master. That’s just my opinion though.