Well, we generally don't have slang for men's dangly bits, more terms to describe their characteristics, if they are noteworthy, eg:
too small:
button mushroom
walnut whip
pencil d*ck
etc
too big (yes, it's possible to have one that is too big):
'like a baby's arm' (courtesy of my friend Paula, who is from Australia and so has a never ending supply of coarse adjectives)
and so on...