I realize that in the movie there was no explanation, but was there ever an interview or somewhere stated where exactly The joker got his scars? or is it one of those things where the mystery is better then the answer?

The latter. It has never been stated. For all we know, they were self-inflicted.

I thought the joker said something about chewing on razor blades when he was a child. I maybe thinking of something else though.

He mentions at least 2 possible reasons how he got the scars, but I think both of his stories were bs. In my mind, they are definetly NOT self inflicted. I think he was doing what he did so well, rippin' off the mob, showing disrespect...and the mob punished him. Moroni, the head gangster in dark knight...said he was "a nobody". I bet he might have had a guess about who the Joker really was...some punk that had shown disrespect and got messed up..whatever the origin, a self - inflicted grin would not fit with my idea of the character.