In November 2012, Matthew Scheidt, 18, was sentenced to a year in prison after he posed as a physician assistant, wearing scrubs and a stethoscope and helping treat patients at a hospital in Florida. He's also been arrested for impersonating a police officer (he allegedly pulled over an undercover cop and told him to fasten his seatbelt).
That may be extreme, but "faking it" seems to be a common human temptation. Watch the full story on Scheidt and other examples on "20/20: Faking It" Friday at 10 p.m. ET - and gauge your inner Matthew Scheidt by voting below.