your bully replies to your tweet with a single period. you don't know precisely what he means, but you do know he's bullying you. You and your bully are adversaries, he's adversarying you. I'm not saying that Shanbehzadeh is the bully, I'm sure it's vice versa, but if you respond to your bully's post with a single period, prepare to get your ass kicked in school the next day.
it might be fun to play the legal game "but what law did I break" in a country with rights and rule of law, but in a country without it...? I'm pretty sure Shanbehzadeh knew what he was risking.