wasn't she in his house as a houseguest when he drew on her face?
that is not even in the same zipcode as funny...
I think, as part of the generation that recently came through college, and NCSU particularly, I can offer a bit of insight.
Having been to two of the three major universities in the triangle, I can attest to the fact that students can be stupid in general. Not intellectually mind you, but on a common sense level. It was not uncommon to see all sorts of displays of this type in the dorms, on campus, around town. While I never participated, found it humorous, or wanted to be around the people who acted like JY and his partying friends, it was not uncommon by any means.
To be clear, I think the peeing on the floor, swallowing rings, drawing on each other's faces... I think they're all ridiculous, and out of line. But they are not uncommon for the crowd that JY never seemed to grow out of. For instance, my sister, whom I love dearly, and is a truly wonderful person, has a tendency to pee on the floor when she drinks. She once did this in front of my parents. My point from this anecdote is not to make excuses for JY's behavior, but to point out that it's not a factor that plays into whether or not he murdered his wife.
There are plenty of other things that can be used to ferret out his guilt, or innocence, such that his party behavior actually detracts from the points to be made.