The teacher's joke was bad form to say the least.... but fercryinoutloud, lets get a grip.
What do you suppose would have been the reaction had a British teacher joked to a class of mostly Moslem students, that if they didn't behave he would spray the class with a can of aerosol pork guts?
Not to mention the trivial little factoid that Palestinians do have this quaint custom of blowing up buses, and that London was hit by same just a few months ago...