I always took for granted that being called a "chicken" was a reasonable trigger to make Marty McFly crazy with rage. I also thought it was normal that the high school teachers wouldn't let him into the talent show because, as they said, "We're sorry. You're just too loud." Why wouldn't they just ask him to lower the volume and let him join the show? Now that I'm thinking about it, it's also odd that guys like Marty and Doc Brown would be such good buddies.