Why are small aggressive dogs labeled nippy but larger ones are vicious?

Why is it that small dogs whom are aggressive and bite are labeled 'nippy' but larger dogs who do the same are vicious? By definition 'vicious' is to be cruel or violent and although the larger dog can clearly do more damage they're both behaving in exactly the same manner. Just because the smaller dog doesn't pack the same punch doesn't make him any less of an asshole. Can't we just agree that they're both dicks?