It is the smallest insect in the world. It can be found on the flea's testicles. This word is not be used literally. It is a personal insult to be used on friends.
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!