Because someone had to.
Yuck, It Wasn't Funny The Hundredth Time is one of those tropes that is disappointingly realistic and I hate when I end up playing it out because it really is kinda mean...
Using "infidel" as an insult doesn't take away from that, though I don't support that religious view. Just as long as he doesn't do anything violent with it, like some Muslims (I assume he's a muslim because they're the only ones who use "infidel" in English text that I know of; Christians prefer "reprobate").