I'm inclined to give the sandwich a twisted smile rather than be offended. Similarly I wasn't offended by the reference to the Troubles, but it gave a frisson to that line which I didn't find in the rest of the film. What I think people will find offensive is not that he's ex-IRA, but the context of it: paralleling real atrocities with the pulpy violence of the movie which is clearly meant to do nothing except entertain us with impossibilities. Ditto with the swastikas.

(And I did wonder how the scene would have played in the US if it had been a Middle Eastern guy talking about watching buildings collapse.)