The term as an insult is nonsensical hogwash - it is used when multiple people are annoyed at the same person for unjustifiable reasons. Win a game against multiple people and cheer? Douchebag! Steal the girl someone else was talking to? Douchebag! Make a profound and compelling argument that stops everyone listening dead in their tracks? Minute to ponder the awesomness of what was just said... oh I mean Douchebag!
It's so transparent, I don't understand how people can take it seriously.