I'd go ballistic tbh, but then I've just been through an extremely stressful time when I was exposed to chickenpox late in pregnancy (I seem to have escaped, but my nerves are shot to pieces, and I think I pretty much sobbed my heart out in fear every single day of the three weeks).
Yes, chickenpox is generally "only" a problem to the baby early or late pregnancy, but chickenpox in an adult can be serious anyway, let alone during pregnancy, with much higher risks of complications associated with it. (Without sounding melodramatic, and I know this is worse case scenario stuff, but some studies suggest up to 40% of pregnant women who catch chickenpox will get viral pneumonia of which there is an associated mortality rate, although I never could find a study that would definitively state the risks I've seen mortality figures between 5%-25% of those catching viral pneumonia).
IT IS A VERY SERIOUS ILLNESS IN PREGNANT WOMEN AND IF YOU ARE EXPOSED WHILE PREGNANT YOU ARE ADVICED TO CONSULT WITH YOUR DOCTOR IMMEDIATELY!
All that said, you have to be extremely unlucky not to already be immune to chickenpox by the time you're pregnant, even if you don't think you've had chickenpox as a child. I still don't think it's worth the risk, and certainly very irresponsible to risk exposing someone to that just because you want to go out to lunch...
Sorry. Am a bit forceful about this subject - probably overly so