At Mario's, the cabbies' favorite hangout, John is admiring a young woman at the bar but lacks the confidence to approach her. Bobby and Tony give him a sure-fire line to pick her up with, "Let's skip the preliminaries - let's get married."
John gathers the courage to approach her and indeed picks her up with the line. When John next shows up at the garage, it comes out that he actually eloped with the woman (Suzanne) to Maryland.
They were having a great time and in the spirit of the pick up line, they were both seeing how far they could play out the marriage joke, until they actually did it. They didn't speak on the ride home, realizing they had made a mistake.
When Suzanne sends John a "Dear John" letter, he decides he wants to stay married to her. John, with help from Alex, then go to Suzanne's family's house for dinner to talk everything out.
John and Suzanne decide to stay married after all.