It is a rare thing to find in New York City, but the woman who sits next to me at work (at a Jewish non-profit) always asks absurd questions and I know they're gonna be good when she gets my attention by whispering loudly, Heeey. Is it offensive to say to a Jew "bless you" when they sneeze?
No. You can even say "Gezundheit"-- but maybe not followed by "Heil Hitler."