Some ways to tell the two lads apart is that Ryan Sheckler is a 21 year-old American known for his large diamond-encrusted Red Bull jewelry, is usually found on a skateboard, and is often nursing a broken bone while surrounded by tan models. He also has "SHECKLER" tattooed prominantly across his back, so you can't lose with that one.
If you are unfamiliar with Justin Bieber or Ryan Sheckler, I salute you. You've managed to live under a pop-culture rock for the past year, and you're most likely better for it.