1.Suppose you are a wicked wicked person, the very type of person that theists like to accuse atheists of being. You cheat on your taxes, you eat children and puppies, and you burn things for fun. You also have sex with men and women in giant orgies, and use a crossbow to practice on living humans. You also torture and mutilate people, and any other horrible thing imaginable.
2. Suppose you are trying to be moral. You do all sorts of good works (remember Game of Thrones? Think of who he's talking to, and how she tried to do all kinds of charity), protect animals/environment, or just generally do randomly kind things.
3. Suppose you just try to live life fully. You build monuments, you go skydiving, bullriding, and try to amend relationships with others.
4. Suppose you are a suicidal. You've concluded that nothing matters, since no matter what you do, nothing really makes a difference in the long term. So you kill off yourself, hurting a few doesn't people who care about you in the process, because you can't figure out how to end your life quietly.
Then you die, and in all cases your body dies, and that's it. In fact, the more moral or fulfilled the life you have, the more of a loss it is. The Jews had a sort of grey afterlife named Sheol, yet even that had a sense that one's life had purpose.
How does one answer the Problem of Purpose for atheism? That is, you say you don't need religion to be moral, but obviously the idea that there is no afterlife actually would tend to revert everything to nihilism, wouldn't it?
. revenge (particularly from Arya Stark).