I have a friend whose husband got up out of bed after a night of drinking, went to the end of it and peed. They decided he had a drinking problem and he went to rehab.
Did you bring it up to him and ask him if he remembers peeing in your room, was it an accident or did he do it on purpose?
We had one New Years Eve at my husband's family's house and his brother peed in the bathroom, but not in the toilet. I really don't know how you can be so drunk that he could still walk to the bathroom, but not know what a toilet was.
Regardless if he was drunk or not, it's not okay to pee in someone's room. Are you sure this living condition is acceptable still? It would begin to feel less so for me at this point. He's an adult. He needs his own place. good luck
It is not always easy to tell how drunk someone is. People are very good at pretending they are less drunk than they are and some people are better at handling alcohol. Trust me, I've been trained on this a lot since I serve alcohol in a restaurant. If u don't know how much he's had to drink (and eat and water) how do you know he wasn't that drunk? I would say that if he's urinating on the floor he's pretty drunk.
He is still at that age where some young people tend to drink a lot, especially on a drinking Holiday like New Years Eve. I hear this story all time: so and so didn't make it to the bathroom they were so drunk. If he is grieving the loss of his father it is even more likely that he is going to cope with it by drinking if that is something he enjoys. If you are concerned that he did this out of spite just ask him. Either way he answers, tell him if he does it again there will be consequences. If he's going to act like a child treat him like one. For instance, if you pay his car insurance threaten to stop if he ever does it again or start charging him rent. I'm sure you can think of something.