When a man, is making love to woman, in the doggy style position, with his right hand, he acts as if he's gripping the throttle on a motorcycle handlebar. With each rev of the imaginary throttle, his thumb hooks down, and is inserted into the woman's anus.
"I was taxing this slut from behind, and I slipped her the Old Kawasaki."
"You have to be careful with the Old Kawasaki, sometimes you end up with brown thumb."
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!