Woo...okay let's see. I do remember hearing of one time during a graducation at the local high school that someone managed to sneak in a live chicken and then another time I think either baby ducks or chicks....and then another where a teacher got mooned.
Now at that same high school when it came time for me to graduate, during when all the students were seated waiting for the ceremony to start, at some point some person started throwing a tortilla around and then later during the ceremony some person or persons managed to sneak in beach balls and started throwing them around all the while trying to prevent the teachers from getting them. xD And then...sllly string got sprayed everywhere.