Atheist Ricky Gervais was sat on a train when he sneezed.
His fellow passengers, out of politeness, said "God bless you".
Rather than debate with them the issue of whether or not he believed in God, he thanked them and continued on with his normal day because he really didn't have the time to get into the whole argument.
However, later on that day, he accessed Twitter, and tweeted about them, behind their backs, to the delight of his millions of followers who laugh at anything Ricky says.