How can you say "this wasn't a funny concept"? Humour is almost entirely subjective. I don't like the jokes and style of Neighbors, it's not to my taste, but I can't say that the film flat out is not funny, because plenty of people did find it funny. Similarly, there are films that I think to be hilarious and others don't.
What do you mean "lose even more money"? This was never going to flop: there's not much competition for it, Rogen and Franco have been consistently successful in comedy, and the controversy in recent weeks had boosted the marketing campaign to amazing levels.