Most likely because by the time Tommy let his nickname slip out he was already well feared by Britain, sufficiently so that coming up with an insulting variant of it seemed a bad idea.
Or he just actively hunted down those that used such names and made sure their deaths were suitably gruesome to discourage the practice. Either works really, and much of Wizarding Britain's population are easily frightened sheep.
Or he just actively hunted down those that used such names and made sure their deaths were suitably gruesome to discourage the practice. Either works really, and much of Wizarding Britain's population are easily frightened sheep.