Trivia: "Mad Dog" Tannen's actions after shooting Marty are a perfect homage by Thomas F Wilson to Lee Marvin in "The Man Who Shot Liberty Valance." He even gets the facial expressions, the mumbled and sarcastic thanks and the jaunty angle with which he holds the gun right.
Trivia: When filming the scene where Marty is being hanged from the clock tower, Michael J Fox agreed to really hang from the rope. Whilst filming, Fox held the rope away from his throat with his hand. At one time he wasn't holding the rope and was really being strangled. The film crew didn't realise, they just thought it was really good acting, until he passed out.
Trivia: Director Robert Zemeckis asked for Clint Eastwood's permission to use his name for BTTF 3. Clint Eastwood felt so honored that he said yes.
Trivia: The band playing at the Hill Valley festival is rock band ZZ Top (two guys with long white beards playing guitar, and a drummer), who wrote songs for the film.
Trivia: In BTTF 1, the first words in the movie are from the radio, and it is an ad for Statler Toyota. When Marty sees the black truck, before he time travels, it is being driven to Statler Toyota. When Marty walks into Hill Valley 1885, there is a billboard in the background for an honest Joe Statler, who buys, sells, and trades horses. Seems like the Statler family has been in the transportation industry for quite some time. (00:26:55)
Trivia: The film was shot simultaneously with Part II. In the five years since the original film was made, Michael J. Fox had forgotten how to ride a skateboard.
Trivia: The automatic breakfast maker that cooks the eggs and the bacon, was designed and created by Simon Wells, great-grandson to the author of "The Time Machine" H.G. Wells, and director of the 2002 remake.
Trivia: The gun that Doc fires at the drive-in is the same gun he tried to fire at the Libyans in the first Back to the Future.
Trivia: Mary Steenburgen had such a good time dancing with Christopher Lloyd for the festival scenes that she overdid it one day and tore some ligaments in her leg. However, (again) because she enjoyed the dancing so much, she chose simply to fight through the pain.
Trivia: The gizmo on the back of the car that is the "Mr. Fusion" is actually a coffee bean grinder. My parents have that particular model. (01:48:00)
Trivia: When Marty and Doc are looking at the map, finding a straight route for the train to take, for a moment the clock (the one that will be put in the clocktower later) can be seen. The time shown is about 10:04 AM. While the time at which it will freeze in 1955 is 10:04 PM, visually the times look the same.
Trivia: The 2002 DVD release of both this film and of Part II is very misframed, with many elements cropped out of frame or not centered properly. The disks were later reissued with corrected framing, and all later DVD and Blu-ray editions have correct framing.
Answer: He simply has an absurdly low tolerance for alcohol, and whiskey is not a wise choice if this is the case. It helps set up the joke when Marty asks the bartender, "How many has he had?", and he replies by telling Marty, "Just the one", as we are meant to think Doc has been in the bar all night drinking away his sorrows.
Jazetopher