The Flintstones: Season 6, Episode 11

6 - 11: The Masquerade Party

Fred and Barney enter a costume contest both dressed as devils. Meanwhile, a new band puts on a radio hoax saying the town is being invaded by space aliens called "Way-Outs". After deciding to let Barney be the devil, Fred decides to dress as a space alien and is mistaken for one of the Way-Outs.