dinky diddydums

“How long have you been ‘Big D’ then?” said Harry.
“Shut it,” snarled Dudley, turning away again.
“Cool name,” said Harry, grinning and falling into step beside his cousin. “But you’ll always be Ickle Diddykins to me.”
“I said, SHUT IT!” said Dudley, whose ham-like hands had curled into fists.
“Don’t the boys know that’s what your mum calls you?”
“Shut your face.”
“You don’t tell her to shut her face. What about ‘popkin’ and ‘Dinky Diddydums,’ can I use them then?”