Your roomate is asleep. You put their hand in a bowl of warm water, and, hilariously, this causes them to wet the bed.
Does this actually work? If so, why?
IME, if someone is sleeping so deeply that you can place their hand in warm water without them waking, they’ve had so much to drink that they were gonna piss the bed regardless.
I’ve never understood this. You took the trouble of bringing a bowl of warm water to the victim. Just pour it on his pants. Success! His pants are wet.
Same with the shaving cream in the hand and the face tickling. You took the time to pout shaving cream on his hand. Just put it on his face instead. It saves you time, and there’s no chance it wont work.
That’s lacking a certain something. The irony of the almost-self-inflicted humiliation.
I’m guessing you were a victim of the ‘stop hitting yourself’ brand of bully?
HAHA!
In sixth grade, during a school trip to Washingon DC, one unluckly soul found himself rooming with the only three of us (all guys) from my school in Oak Ridge, Tennessee.
We tried the water trick. It didn’t work. So we poured it on his crotch, woke him up, and told him that he had pissed the bed.
The next day, we won our right to a mono-school hotel room 
Often, if I’ve been out in the cold, as soon as I come inside to the warmth I get a desperate need to go pee. I always figured this was the same principle at work.
Heh. You are going to fit in well here.