Ask for a half and half. That seems to be less offensive. Dublin people do seem to object to the black and tan thing. Probably all these bloody Sinn Fein supporters in the working class areas!
I've tried to make a few half and halfs but never got the desired visual effect or taste. Tried Smithwicks, Guinness, Harp and I think Murphys. I suppose the problem is starting off with piss-poor ingredients and then sure why waste a €3.50 500ml bottle of some nice stout on a gimmick!