John Ritter's dance number in "Up In the Air" at a cocktail party where Jack Tripper who's loopy from mixing tranquilizers to calm him on a small plane ride and alcohol at the party. It's a tour-de-force.
When Roeper mocks gay people for being "interior decorators", Jack points out that some gays are also boxers. When Roeper expresses doubt that a gay person would hit another guy, Jack says "Only if they make fun of us" and cracks his knuckles.
Also a Crowning Moment of Heartwarming : In Season 6, Jack mistakenly serenades a woman named Bernice instead of his evil blonde girlfriend, Arabella. Bernice gives a speech about their romantic Meet Cute, and it's clear she Thinks Like a Romance Novel. In the next scene, when Arabella makes fun of Bernice, Jack stands up for Bernice and repeats her romantic speech, and then he kicks out Arabella.
Arabella: I never want to see you again.
Jack: Frankly, my dear, I don't give a damn *slams door*