What Makes Someone A Role Model?

Yesterday, on our Facebook page we talked a lot about Justin Bieber. People had both negative and positive things to say about him. This actually got me thinking about role models. A lot of people criticize people like Justin Bieber and Rihanna because they are being "bad role models". My questions is: When did they ever say that they were role models? Just because someone is in the public eye does that automatically mean that they are supposed to be good role models and have to act a certain way?

In this Nike ad, Charles Barkley delivered a similar idea, take a look: