A redundant and pretentious way of simply doing the right thing while feeling the need to have it justified and announced by being part of a group/clique. Often marked by the 'sXe' tattoo, sometimes just the 'X' mark.
"Do you want a smoke?"
'No way! I'm straight edge! I don't do that sorta shit!'
"You're pretty high and mighty for an under age kid with a tattoo!"