In the episode "Provenance", Dean, Sam, and Sara are back at the old woman's house after her death investigating the evil portrait. Dean has a photo copy of the painting, and is comparing it to the actual copy. He notices that the razor in the photocopy is closed, while the one in the original is opened. He then says to his brother, "Jared, check it out." In the show, Dean's brother's name is Sam, not Jared. Jared Padalecki is the actor who plays Sam.

If you are not paying close attention, Dean's words could almost pass for a 'Sam', but listening carefully, he does indeed say Jared. Jensen Ackles(the actor who plays Dean) and Jared Padalecki are good friends in real life, so this slip up is understandable, but cute none-the-less.