It's when you are really going for it - whether it be at work (doing a big deal, showing your expertise or kicking somebody's ass who made you mad) or showing off at Sports or with the opposite Sex.
You're showing the world that you are the man (or wo-man)...
... oh man, did you see Benoit at Crossfit yesterday. He was REALLY CROC'ing out!
.. Hey, you ready for the meeting? Hell yes, let's Croc Out!
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!