Episode: 5×18 (Season 5 Episode 18)
Name: Meet the Quagmires
Originally Aired: May. 20, 2007

Plot: Death grants Peter’s wish of going back in time to be 18 again just for one night so that he can sow his wild oats. In 1984, he bails on a date with Lois to go to a bar and make out with a movie actress, but when he returns to the present, he discovers that he is now married to the former starlet and Lois is with Quagmire. Source: Fox