Well, I expect it's something of a shame, for him, that he decided to insult someone else's symbol in an extremely grave fashion before finding out just what it meant to them.
Again, what I want to stress is not that the flag was Israeli and thus somehow ought to be more "inviolable" than other flags, but that the flag belonged to the Jewish kid, it was apparently in his room, and it did not belong to the offending student: that student had no right to do what he did. And the fact that he did it to the possession of a foreign kid, whom he ought have expected to have cultural differences that might attach to the things he owned or valued, simply demonstrates to my mind that it was a knee-jerk act of intolerance.
It's interesting to me to hear that British people apparently don't feel attached to or overly respectful to their national symbols of cultural heritage and identity.
But even if I did not know this, and I were a visitor to Britain, my presumption would be that such things were respected, and that it would be taken amiss for me to walk into someone's space, take their flag, and use it as a hanky for my junk. Call me old-fashioned, if you will, but it seems to me that it is safer to presume that something that someone owns and displays, which reflects some element of their culture and national identity, is likely to be valued-- perhaps even significantly so.
How is it not natural, especially when dealing with people from other cultures, to presume that respectfulness is a good place to start from, until one has a better sense of where their values and beliefs fall out?
I don't mean to suggest we all ought to walk on eggshells around one another. But there has to be such a thing as basic respect and cultural courtesy. And this isn't a case of someone speaking a little too frankly, or making some similarly small faux pas. He walked into the guy's room, reached into his own pants, felt up his own meat and two veg, and rubbed his hands on the guy's flag. Short of actually taking a whiz or a crap on the guy's flag, it's hard to think of anything more likely to be offensive to the guy's flag, and clearly, the flag means something to the guy, because it's on display in his room. Precisely what gap of cultural knowledge would make it surprising that, if he did something incredibly offensive to another person's displayed flag , that might be taken as unacceptable?