Damon isn't heroic. Not in the broad sense. There's nothing heroic about a man who murders when things don't go his way or who will sell a friend down the river if it suited his purpose well enough. Damon is tempestuous and that doesn't exactly make for heroism. But while Damon isn't heroic in the general sense and while he isn't about to lay down his life for the greater cause if he can find a way out of it, there are times when Damon is a hero. Or, better said, there are certain people for which Damon is willing to be a hero. Stefan and Elena. His brother and the girl he loves. He makes sacrifices, lies, and kills for them. While that doesn't necessarily seem heroic, there is one thing he does that helps him make the hero cut: he saves them from themselves. Damon does what needs to be done to save them from their own (poorly made) decisions and martyr complexes, despite how damaging it can be to his relationship with them. He's Stefan's hero and he's Elena's hero and that's what makes him heroic.