Here's a Catholic Problem for you.
You're one of the last people in line to receive communion and the chalice only has a few drops of the Blood of Jesus left. Even though the Blood should be self-cleansing (like soap!), you're a bit grossed out by the fact that this is backwash from the however many congregants there were before you. But then you only sip half of the few drops that's left because there are still a few people behind you and you don't want to be that guy who drank all the Blood, but now have perpetuated the same problem for the next person. It would be uncharitable to jokingly (let alone seriously) cough for good measure.