Maybe the people around you are just twats but I know many people born and raised in Canada/USA who have Irish accents and they aren't just putting it on. There are large Irish communities in England, USA, Canada, many countries and if you are raised within those communities then you can easily have an Irish accent without stepping foot in Ireland.
This whole discussion is pointless, Jack is Irish and English and he will choose who he wants to represent when he deems fit. No one of us can say what he is or who he should play for, only he can.
This is a good piece by an Irish Brummie who supports Villa just like Jack.
http://www.balls.ie/football/292616...ink-twice-about-jack-grealishs-dilemma/292616
What I like about this too is it points to multi-nationalism. Many people are from 2 or more countries and feel proud of both/all and there is no choosing between them. Jack's brother has said before that Jack is proud to be Irish and English and if he wasn't a top footballer no one would bat an eyelid but since he is he has to choose. Even when he does choose it doesn't make him only one nationality, he can still support and be proud of being both English and Irish.