An internet hardman is someone who goes online in chat rooms, message boards and the like and insults, belittles and abuses other people. His avatar will probably be some image that gives the impression he's a hardcase, and he'll probably have some tagline like "Shut the fuck up" or "Who you dissin" or "When the master's talking you shut it". But if you were to meet this person face to face you would probably find he is either a skinny or dumpy nerd with thick glasses and his vest tucked into his skidmark-stained y-fronts, has no social life to speak of, has a relationship with a collection of porno mags and has never spoken to a girl.
"I am the Internet Hardman. You are a sad loser and an idiot".
"Fuck off back to your smelly bedroom, you no-life waste of space".