First being somebody who is overly abrasive and all too willing to show off their physical power (most of the time in a little scuffle). In laymans terms, the guy who thinks he's hot s**t and wants to to take it out on the other guy.
Where I'm from, this is often the popular definition of hard. It's all false bravado, perpetrated by guys who didn't have a man to tell them or show them what it truly means to be a man. Yes, that individual may whoop many an arse in street fights but at the end of the day they're left with nothing but the adulation of others like themselves and bruised knuckles.
Navy Seals, SAS, French Foreign Legion training in the Amazon, a father standing up to gang members trying to recruit his son(s), a mother doing that same thing, a fighter stepping into the ring with an opponent that everyone (and on paper) says is a heavy favorite and giving it everything....that's 'hard.' To me 'hard' is all about mental toughness.
Here's my personal anecdote on 'hard.' I have a friend who was a Marine Scout/Sniper. When he was going through training to make it into SF, he was told that the Marines weren't looking for the biggest man....they can make you into that. They weren't looking for the strongest or fastest man, they can handle impart those qualities with the training as well. What they were looking for was the guy who wouldn't quit. Under the type of training they put you through, that particular quality can't be taught.
or.........what Matski said. Lol.