Wild Hogs

Doug Madsen (Tim Allen), Woody Stevens (John Travolta), Bobby Davis (Martin Lawrence), and Dudley Frank (William H. Macy) are four middle-aged suburban men living in a Cincinnati area suburb who find themselves frustrated with the pace of daily life and lack of adventure. Doug is a dentist who has trouble relating to his son Billy (Dominic Janes), Dudley is a single clumsy computer programmer who is afraid to talk to women. Bobby is a henpecked plumber whose wife has made him return to work after having taken a year off to unsuccessfully write a book, and Woody is a rich lawyer married to a supermodel. They find escape from their daily routines on weekends by riding motorcycles together posing as a biker gang called the "Wild Hogs".
One day, when Woody finds out his wife is divorcing him and leaving him bankrupt, he and his friends go on a road trip on their bikes to California. After encountering several misadventures, they end up at a local bar, where they meet a much larger biker gang called the Del Fuegos, headed by Jack Blade (Ray Liotta). Jack calls the Wild Hogs "posers" and has his gang take Dudley's bike after a bogus deal to exchange Dudley's bike for a new bike that is in fact old and derelict, forcing the men to leave with Dudley in a sidecar attached to Woody's bike.
Outraged at their actions, Woody returns to the Del Fuegos bar and retrieves Dudley's bike, cuts off their bikes' fuel supplies in the process and fabricates a story to the other Wild Hogs of how he "negotiated" with them to return the bike. When the Del Fuegos hear the Wild Hogs riding back past the bar, they attempt to pursue them, only for the bikes to stall. Jack inadvertently drops his lit cigarette onto the ground, igniting the fuel leaking from the bikes which then causes the the bar to explode. Woody, after witnessing the explosion from afar, convinces the others to keep riding. Eventually, the Wild Hogs run out of gas and end up in Madrid, New Mexico, where they stumble into a diner and help themselves to water and beer without first paying for the beer. As a result, the townspeople first mistake them for Del Fuegos. When the Wild Hogs explain their actions, they learn that the Del Fuegos have been terrorizing the town frequently, while the local police force are unable to do anything to protect the town. Although Woody is still antsy about the Del Fuegos, the others convince him to stay in the town overnight. During their stay in the town, Dudley falls in love with Maggie (Marisa Tomei), the diner's owner, while out searching for the Wild Hogs, Jack's closest biker members Red &amp; Murdock spot the group and report their location to Jack. Jack tells the pair not to hurt the Wild Hogs until he gets there. Bobby spots Red &amp; Murdock before confronting the pair gets splashing beer and spraying ketchup and mustard on their clothes before finally laying two uppercuts to the Del Fuego members leaving them unable to fight back. The Wild Hogs are hailed as heroes amongst the town's residents and celebrate well into the night with the townspeople.
The next day, Woody persuades the others that they must leave, but their departure is ruined when the Del Fuegos arrive. Jack threatens to attack the town unless the Wild Hogs pay for the damage done to their bar. Woody admits to the Wild Hogs what he really did to get Dudley's bike back as well as the real reason for the trip, upsetting the others. Jack and the rest of the Del Fuegos take over Maggie's diner, but when he threatens to burn it, Dudley confronts them and is captured and tied from a rope against a tree. The others attempt to rescue Dudley but fail. They then decide to fight the Del Fuego gang letting Jack, Red, Murdock and a member trained in martial arts battle the group in a 4 on 4 fight but the Wild Hogs are repeatedly beaten down. The townspeople band together to battle the Del Fuegos, but just as Jack threatens to take on the rest of the town Damien Blade (Peter Fonda), Jack's father and the founder of the Del Fuegos, arrives and stops the fight. Blade lectures Jack for letting four "posers" hold off an entire biker gang, questioning aloud just which side was the "posers", and saying that the bar was merely an insurance scam and therefore he was glad that the Wild Hogs destroyed it. Blade tells the Del Fuegos to leave town and ride the open road until they remember what riding is really about, mentioning as he leaves that Jack "takes after his mother."
Doug and Bobby's wives arrive, and Doug reconciles with his son. Bobby's wife orders him to return with her, but he refuses and convinces her to let him finish the ride. The Wild Hogs leave and arrive in California. During the credits, it is revealed that the Wild Hogs called Extreme Makeover: Home Edition to give the Del Fuegos a new bar and watch the event on TV.

Question: What causes the bar to explode?
Answer: Jack drops his cigarette; Jack drops his cigarette