What the Fallacy?!
Appeal to Authority
The Fallacy
Using the opinion or position of an authority figure, or institution of authority, in place of an actual argument.
Why it's wrong
Much of the time experts have better information and understanding than other people, but holding a position of authority doesn't necessarily mean that someone is right. After all, the highest medical authorities used to think that bleeding sickness out was a good idea.
Example
The toothpaste commercial claimed their brand was superior because a famous actor, who plays a doctor on TV, said it was the best choice for oral hygiene.