I was disturbed by that too. I called up my friend (who is my age btw and I am 20) and while talking about Rihanna she actually started laughing. "Dude, I wonder what she did to piss him off like that! Hahaha!" My reaction: ??? Huh???
I think that violence is such a big part of movies/TV that when a celebrity (and I think it has more to do with her being celebrity than anything else) goes through something like this, it is seen as a joke. It's easier to laugh at because she's a celebrity...not a "real" person. It's all part of the TV/movie personality.
If it had been a real person, a friend of these kids, I doubt they would've been laughing.
I'm "TechKnockout" now.