Spike is my favorite tough dog name. Other tough names include Bruiser, Killer, and Ranger. Any name that can be connected to a famous Hollywood tough guy would work,too. These include Rambo, Duke, Mugsy and Bogie. Any rough weather name could also work for a tough dog - like Hurricane, Tornado, Thunder and Lightening.
As my family loves dogs that most others find intimidating, it has been a tough job finding a good name, however, our little boxer puppy which will grow up to be a rather large intimidating dog is named "PUDDLE DUCK". The first time someone sees her after I call "Puddles" from the back yard,(full grown) the reaction will be priceless.