I imagine that's a bit easier to say if the joke isn't ALWAYS about you though.
(I'm not a ginger by the way )
Joke isn't ALWAYS about ginger kids though is it. I remember, as a kid, that ANY feature was used to pick on you. Tall, small, fat, thin, ear size, hair style, hair colour, face shape, upbringing, parents car, parents hair colour, parents choice of garden shrubbery. There's a whole raft of cards out there that put posh old fashioned people in a bad light, should they be upset too?
There IS a line, but I don't think that card crosses it. There's a difference between something being used as humour and something being used in spite. Turn it round and say "northern kids" or "blonde kids" and I wouldn't give two hoots, in fact I'd probably laugh out loud despite having been both.