[SuziQ]

I said it twice to a lady who sneezed twice, as I was standing in line on a plane, waiting for folks to find their seats. She just smiled and said "Thank you".
She had sneezed once, and I said "Bless you". She sneezed again, almost immediately, and I said "Bless you, again". Folks around us kinda chuckled.

[Yardstick]

Well, that’s always the dilemma isn’t it. The first sneeze qualifies for a “bless you” but what about subsequent sneezes? You have to draw the line somewhere. After some number of sneezes the sneezer is on their own. But figuring that number is a tricky social calculation. It has to be done on the spot and basically by the seat of the pants since there really isn’t much guidance on the subject out there.