A dominant person who is calm when unprovoked but can get very aggressive and try to break your legs if you step on his toes or insult him or his family/friends. Very close friends will not use the name Bossdog but general friends and good friends will.
A hardo is a person who tries extremely hard at everything. Most times a hardo will try very hard at things that do not require excessive effort. For example, sports practices, gym class, etc.
Wow did you see Jack at practice today? What a hardo!