No matter what seniors (high school or college) are told, the graduation ceremony is not really conducted for them. As with weddings and funerals, the performance is for their relatives, which means it must be pompous and dignified. And that means no throwing food.
Which is why the mid-year commencement ceremony at my alma mater, the University of Arizona, has been canceled. It seems that a tradition has developed whereby the audience throws tortillas during the graduation proceedings. As you might expect, the people running the place just couldn’t allow anything that undignified at such a solemn occasion so they were forced to cancel. I guess they couldn’t find any flour/corn detectors for the doors.
Of course, I never attended my graduation program so I couldn’t tell you if there was any tortilla flinging that year. But since graduation is really for the relatives and the tortillas are coming from the audience, why not build the tossing into the ceremony? It would certainly be a uniquely southwestern affair. Just make sure the tortillas are not too stale or they might hurt someone.
Incidentally, they didn’t cancel the commencement for Masters and Doctoral candidates so I can only assume that group is too dignified to have tortilla-flinging relations. Or they spent so much on the degree that they wanted to soak in every dime of the pomp.