The question about “the Jews” being responsible for the death of J isn’t a joke and it often isn’t individual anti-Semitism. For many Xtians it’s a matter of religious belief, like 2+2=4, and not a personal matter at all. If he’s not saying it to your face and he’s not trying to be offensive, don’t react. It’s only recently that the Catholic Church has officially stopped holding the Jews (all Jews) responsible for the crucifixion. Xtianity was until recently openly anti-Semitic. It’s only in the last hundred years or so that many groups have become a little broader-minded.
Many of the people I went to public school with think I’m “going straight to Hell” along with all other Jews and anyone else who doesn’t “accept J.” It’s difficult to get one’s head around this sort of thing, but after all we’re in Golus. It isn’t all Xtians, and many of them mean well. Juzt make a little psychological space and don’t get too shocked.