This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Planes, Trains and Automobiles
Del's "the real deal" speech is as sad as it is beautiful. You get the impression that he's probably had this exact conversation many times before.
Del's breath is noticeably shorter when Neil insults his "boring stories," like he's about to cry. He could take the attitude and the threats, and was even willing to argue at first, but as soon as Neil made it personal, it hurt.
His line about how his wife likes him is especially sad once you learn she's not alive to any longer.
Del's monologue to his dead wife about how much of a screw up he is while sitting in the burnt-up wreck of a car, just as it's beginning to snow. Not only does he know he has problems that needs to work on, but it implies that things weren't so rosey between them when she died.
"The movies that last, the ones we return to, don't always have lofty themes or Byzantine complexities. Sometimes they last because they are arrows straight to the heart. When Neal unleashes that tirade in the motel room and Del's face saddens, he says, 'Oh. I see.' It is a moment that not only defines Del's life, but is a turning point in Neal's, because he also is a lonely soul, and too well organized to know it. Strange, how much poignancy creeps into this comedy, and only becomes stronger while we're laughing."
Plus, the Wham Line: "I don't have a home. Marie's been dead for eight years."