This is not a new tactic. When I lived in Europe in the mid to late 80's, in the height of Reagan (my hero) this was a common practice of the lefty American tourists from CA, the west coast and other crunchy places.
Me, I'd have tattooed the American flag across my forehead....
Cowards to the end...
The soccer hooligans don't care if you're a lefty or a righty......but my son was a soldier and listened to the advice but NEVER pretended to be anything other than a proud American.