Marie and Jess
Harry and Sally set each other up with their good friends, Marie and Jess, intending for Harry to be with Marie and Jess with Sally. Ironically, Marie and Jess fall for one another on the double date and eventually become engaged.
30 seconds to all night
Harry and Sally have sex, and he has the opportunity to stay with her through the night and have the opportunity to further their romance. Ironically, he leaves the next morning distressed. We see that Harry is the common denominator in his misery from this.
Harry and Sally
The entire relationship between Harry and Sally is ironic. For years they continue to bump into one another and it's clear that Sally is not interested in Harry though they are friendly. The irony is that they end up getting married over a decade after they took the car ride from Chicago to New York together.
A Shot
Harry's wife tells him she wants a trial separation, that they can still date to see if anything is there between them. Ironically, she's already booked movers to come get all of her things out of their apartment so she can go live with her new boyfriend.
Friends
Harry tells Sally that men and women cannot be friends because sex gets in the way. He says this on their drive to New York. Ironically, years later he asks Sally to dinner "as friends" and claims he never said that men and women can't be friends.
