From TVGuide.com:
Even the biggest goody-two-shoes has a repressed bad boy in them somewhere deep down. Just look at Sam Winchester (Jared Padelecki). When Supernatural started, Sam was about as sweet and innocent as a person could get and even though he would chide his brother Dean (Jensen Ackles) for his love ’em and leave ’em lifestyle, it was clear he also secretly admired big bro’s tough guy attitude. Of course, a few seasons into The CW drama, Sam’s inner bad boy was eventually revealed in full force, proving that he wasn’t as different from Dean as he originally thought.