A tushhog in the South is an old guy who always finishes fights. A tushhog bar is a bar with these guys in it and NO ONE starts trouble in there with these guys. Size or physical appearance has nothing to do with these guys, they are just insane fighters. The name itself comes from the the fact that old boars have very long tusks (tush) that they can cut anything up with. The other definition in the Urban Dictionary is totally wrong and would probably be laughed at in the South. In fact to call someone a "tushhog" is a sign of respect and never an insult!
Don't mess that dude over there. He is a real tushhog.