I guess the implication is that by chucklevoodoo'ing the clown doll into John’s head, Gamzee is - by way of persona alchemy - ’interpreting’ John as a boy, in essentially the same way Caliborn ‘interprets’ his favourite minions (leprechauns, clowns) as boys… Gamzee never seems to aim any animosity at John in particular, and their joke appearances together in Zillyhoo-related flashes suggest a kind of kinship, so it really seems like it could have been given as a badge of honour more than anything else