Someone that tries to look rebellious and impress others by doing irrelevant things such as pocketing chewing gum from the 99c store or throwing screwed up paper on the ground. They will be too afraid to do anyrhing actually rebellious.
Rebel tryhards will scare easily and run off in a panic after doing what it is they do.
Joe: omg let's run! Did you see me kick that empty trash can over? Hope I don't go to jail...
Jim: you rebel tryhard..