On Thursday, December 11, 1980, CBS premiered the original Magnum P.I.
The two-part Don't Eat the Snow in Hawaii was up against Games People Play (with Greg Evigan as one of the guest stars!) on NBC. The short-lived reality program focused on unusual sports was intended as actors-strike-friendly programming.
ABC's comedy lineup consisted of Mork and Mindy, Bosom Buddies, Barney Miller, and It's a Living.
At 10:00, it was Knots Landing on CBS and Number 96 in NBC. The latter lasted even less time than Games; it was a tamer version on a very popular Australian prime-time soap. It ran Wednesday, Thursday, and Friday of this week as a launch stunt.
If you weren't interested in the soaps, you could turn on ABC and see 20/20 with Geraldo Rivera ripping the lid off of heroin trafficking. According to the description on Ultimate 70s, Posing as a buyer of heroin in Afghanistan, he traces the drug from its source, through western Europe, to the streets of America.