My husband is (well he has now renounced but that isn't relevant) American but has lived in the UK for 25 years or so now. I have to say it does irritate me that he still uses American vocabulary almost in its entirety. I can understand that that's his instinct but sometimes someone will just clearly not understand him and he will just keep saying the American term and I get a bit frustrated that after all this time he can't at least notice why they're confused and use the British term.

I realise this is a bit tangential to the OP.