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Either punch him in the face [Probably not the best course of action]
Or report him to the people in charge of the tournament.
People who think that because they can get away acting like that on the internet they can do it in real life are going to have reality break their nose sooner or...
I was about 7 and I just got off the S.S Anne after getting the Cut HM. The ship set sail and I thought I just broke something (Because in the Anime, they stay on the ship as it's sailing). I started crying because I thought I just failed the game and there would be no way for me to continue...