Now someone explain to me why it is forbidden to attack another player when they are online?

Huh? It isn't. You can attack them anytime...

I figured as much. I was attacked by a much larger player than me and seen it coming.. Thus, I vamped..lol He messages me later complaining about not notifying him I was online... I was like wtf!! You are attacking me!!lol

He probably meant that he'd have recalled the attack if he knew you were on. It's always a good idea to do that, because some people are good sports.

Sakorn you should learn about the ninja