Well this might sound odd coming from me, but understand that all fantasies of violent retaliation are just that. If nothing else in such a situation remember they have more witnesses than you do if nothing else given that your disliked. The authorities being people to might also disagree with them on some fundemental level.
*THAT* said, I can't comment too much on Ginger predjudice because it doesn't really exist here in the US. Red Hair is nothing special (and is considered very nice on women), we celebrate Saint Patrick's day, and where Irish were once discriminated against it's now considered to be fairly cool.
That said keep in mind that the whole Irish occupation thing didn't "end" that long ago and there are still tensions. What's more it's not a simplistic thing of the "England Invaded, they are wrong, they should get out" like some people would like to make it. I'm not picking a side really, just saying that there are reasons for hard feelings.
I guess the best way to deal with it is to relax, roll with the punches, and basically adapt. I think the situation will change given enough time. Heck there was once a time in the USA where people used to put out jobs and have "Irish Need Not Apply".
Try and be a nice guy in general, remember things will improve when your dealing with more adults (I'm guessing these are teens), and honestly it might not hurt if you did Dye your hair or something as ridiculous as that might sound.
It's a wierd kind of situation where violence, or vehemently refusing to adapt, is likely to just make the problem worse.
Not quite the great civil liberties message of our time, but I believe that in many cases, beyond a certain point you can't force change and tolerance. You have to wait for time to pass.