How to punish my nephew?

So I'm a single guy and my brother and his wife went on a last minute vacation and left me with their son. Hes 11 and we only see each other like 10 times a year but he thinks of me as a "cool uncle". Anyway he has an iPad mini that he is on all the time and I try and get him to go out on my boat for the night (it's a cabin cruiser) but he doesnt want to. I ask him what he wants to do and he just wants to play on his iPad. Well he told me he can watch YouTube so I took his word for it until my brother called me that night and he said he isnt allowed to use it. So stupid me instead of telling him no YouTube I just turned off my internet and he threw a huge hissy fit so I let him calm down and now hes making it look like nothing ever happened. How can I punish him?

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