I was half teased/half shitty-passive-aggressively told it's rude to not say "God bless you" after someone sneezes. I never say that. Never have. I think it's one of those things people say and they really have no idea where/how it originated but it's been adopted as a common courtesy or considered polite.
So, my rebuttal; Gaaaaaawd, you're annoying and fucking frittata. I hope your sneeze frees your soul and the devil snatches it, or the devil gets into your body or you get the plague - or whichever origin you realize "God bless you" came from. The polite thing to do is not fucking sneeze on me and be a grown up with your itty-bitty, fragile feelings and not pout when someone doesn't notice your sneeze. Baby.