A combination of scrote and shmohawk. It has nothing to do with hairstlyle, it is just a good way to switch up insults and can apply to a wide range of people, usually men.
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!