Gesundheit

I always say “shut up” in the most annoyed way possible.

Instead try this: Say “What?” And stare at them. Wait for them to explain. Act as though you do not know what a sneeze is. Allow them to explain the process of a sneeze. Tell them you have never experienced that in your life. Wait for them to get exasperated then in a dismissive way mention that you aren’t sure you believe them, and change the subject.

Congratulations, you have won this interaction.