That's exactly what I thought until Carmen set me straight. (Thanks, buddy.) It's any image that a reasonable person would recognize as the flag, with an exception for uniforms for the military, firemen, police, etc. And I have to admit that, thinking back to my childhood, no one would have worn any representation of the flag, except hippy chicks on the back pocket. (That brings back some good memories!) Personally I too am fine (in fact, more than fine) with flag tee shirts, but that's preference; Carmen actually knows the flag etiquette.
I'd like to see a link to support this. It defies common sense though as it suggests Olympics athletes are disrespecting the flag by having it on their jerseys.
And in any case, this is not about the school being worried about flag etiquette. We all know this is about Mexicans actually try to impose their culture OVER American culture on American soil (and maybe some idiot administrator). It's just amazing that they have the audacity to do this when Mexico is a complete shit hole. Do they purposefully want to turn this country into a shit hole too?