Can you imagine a rape victim who's being questioned about what she remembers from the attack yelling "I like beer! Everyone likes beer" and being taken seriously?
He refused to answer questions pertaining to establishing what the truth is.
Also, he started his defense by saying that an assault such as what Dr. Ford described would hypothetically have had to take place on a weekend and saying that he's proven that he was almost never in his hometown on the weekend. Soon after saying that, while describing his weekly routine during the summer of 1982, he said that there were weeknights when he had some beers with his friends. When he said that, I thought I could see from his face that he knew he had contradicted himself.
Dr. Ford had previously clarified that the attack didn't take place during a party, that it was during an informal gathering of a few people, at which Brett Kavanaugh and Mark Judge were drunk. She went out of her way to clarify that; I wasn't sure why, and then when Judge Kavanaugh made his mistake, it made her earlier clarification seem significant.