other than the obvious, mr potter (harry) or just mister :
rat dog (my dad wasnt a lover of small dogs - he is now though)
flea bag ( my dad again)
poo face ( as i saw him run into his own poo one day with his nose to the ground
)
big/little man depending on brave hes being
'mummys little baby' is about the worst.
i think i call him Harold more than harry at the moment - but perhaps thats because he is always doing something he shouldnt