I'm going to wake my friend up with a glass of water
Why are you going to be mean about waking him up?
He promised me to wake up at this hour.
I think that you should find a better way to wake them up. It is rude to throw water on a person that is sleeping.
Well, I have to wake him up some how.
Waking someone up with a glass of water is rather harsh. Just nudge them and they'll wake it. Otherwise, you're just looking for a fight.