so today is Yom Kippur, the holiest day in the Jewish calendar. when you think about your sins in the last year, and try to atone for them. Or something like that, take everything I say with a grain of salt since I'm Catholic and don't know exactly what I'm talking about.
Which gets me to my next point. Yom Kippur is one of those days, like Good Friday or Veteran's Day - it's somber. You want to acknowledge that you know it is going on, but it doesn't exactly go with the adjective "Happy" in front. I think Isaac has told me in the past that you say something like "hope you have an easy fast", but of course that would sound a lot better in Hebrew. So would things like, "Hope you remembered and atoned for every sin!" or "Let's all sin less this year!"