You are asking for a level of evidence that anyone would normally ask for... Kavanaugh lying about being a drunk is supported by statements from his classmates, roommate, his own yearbook, and his bar fight. We know for a fact that Kavanaugh tried to present himself as a casual drinker with no problem with drinking, while a lot of people and some incidents came out pointing at a much more severe level of drinking. Other people did not agree with him. They specifically came out and disagreed with him to the level of calling him out lying under oath.