The next day, Harry is ready to go by noon. Vernon and Petunia are uptight and irritable while Dudley skulks around fearfully. Nobody eats much at lunch and Vernon confirms that the Weasleys will drive to get Harry. He spends most of the afternoon in his bedroom but as the appointed hour approaches, he heads downstairs. Harry and the Dursleys sit for a half hour, at which point Vernon snarls that the Weasleys are late. As he and Petunia mutter, they hear loud noises coming from behind the boarded-up fireplace.
Vernon's insistence on his version of normalcy (driving, being exactly on time) shows that he has little capacity to understand others' ways of living and moving through the world, especially people like wizards whom he already looks down on. Again, this gives Harry one objectively bad role model as he begins to grow up and come of age.
Harry hears Mr. Weasley tell Fred and George to go back. The Dursleys angrily turn to Harry, who explains that the Weasleys are traveling by Floo powder. Harry explains to Mr. Weasley that the Dursleys have an electric fire as Ron arrives in the fireplace behind the boards. Mr. Weasley tells Harry to stand back and blasts open the wall. Aunt Petunia shrieks as Mr. Weasley warmly approaches her and Vernon to shake hands. Fred and George run upstairs to get Harry's trunk as Mr. Weasley tries, unsuccessfully, to make small talk about plugs and "eckeltricity."
Having to bridge the gap in culture between Muggles and wizards shows that Harry has other times in which he has to think about things from multiple angles. As someone who does live in both worlds, he has to be able to understand how Vernon interprets people suddenly appearing in his fireplace, as well as Mr. Weasley's fascination with electricity and Muggle technology.
Dudley sidles into the living room clutching his backside. He refuses to answer as Mr. Weasley tries to kindly ask him about his summer vacation. As Fred and George return with Harry's trunk, Mr. Weasley lights a fire and tells Fred to go first. Before Fred steps into the fire, he drops toffees and scrambles to pick them up again. George goes next with Harry's trunk, followed by Ron. Harry bids the Dursleys goodbye as he steps towards the fire, but Mr. Weasley stops Harry and incredulously calls Vernon out for not saying goodbye to Harry.
When Mr. Weasley takes Vernon and Petunia to task for not saying goodbye to Harry, it positions him as the exact opposite of the Dursleys: he believes in behaving empathetically and kindly towards others, no matter how much one may or might not like them. His attempts to engage Dudley in conversation also situate Mr. Weasley as a positive role model.
Just as Harry steps into the fire, he hears gagging and sees Dudley kneeling, gagging on his tongue, which is now a foot long. Petunia and Vernon fling themselves at Dudley and Mr. Weasley approaches with his wand to help, but Petunia shrieks in panic. Vernon starts throwing things at Mr. Weasley, who finally yells for Harry to leave.
Petunia and Vernon's desire to not let Mr. Weasley help is understandable, though whatever happened to Dudley is clearly the work of magic. This indicates that the Dursleys aren't willing to think critically about what's in front of them to get Dudley the help he needs.