He has
criticised Johnny's decisions at times (eg. leaving the Smiths, 'giving in' during the court case), but he has never said anything truly harsh about the man himself. Certainly not by the typical (terrifying) standard of Moz insults.
"Tragic Ethel is of elephantine proportions and destined to die alone, smelling of attics", "David feeds on the blood of living mammals", "So-and-so slithered, snake-like, up to me and said...".