In contrast to a gutter slut... high heels, miniskirt, smeared makeup, and a martini glass. A ditch slut would have jeans, tshirt, no teeth, beer can, and be barefoot.
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!