"Christmas and the Hard Luck Kid" (1970)
Mary's deep into the holiday spirit, but she gets stuck working Christmas Eve and Christmas Day. Cut to Mary dancing alone in the office and chatting with a stranger over a transmitter. (That stranger, by the way, is voiced by Henry Corden, the man behind Fred Flintstone.) Lonely, scared, Mary is in despair, until... Well, surprise. Best line: When Rhoda asks Mary, "Why don't you hang out panty hose; they hold more."
Pictured from left: Ed Asner and Mary Tyler Moore.