It seems that he wanted to try not being a good person, at least once, by assaulting a girl whom these then-girls didn't know.

https://www.judiciary.senate.gov/imo/media/doc/2018-09-14%2065%20Women%20who%20know%20Kavanaugh%20from%20High%20School%20-%20Kavanaugh%20Nomination.pdf

Sometimes people don't know when they're being funny:  "Many of us are not lawyers," the letter says.

He knew that many of you would be lawyers, though, or that you'd have similar professions or marry men who did; that's why he and his friends were always respectful of all 65 of you. 

Only men who routinely target women who have little to no social power can attack 65 women or hundreds of women and never be confronted about it.  

https://www.washingtonpost.com/investigations/california-professor-writer-of-confidential-brett-kavanaugh-letter-speaks-out-about-her-allegation-of-sexual-assault/2018/09/16/46982194-b846-11e8-94eb-3bd52dfe917b_story.html?noredirect=on&utm_term=.5e31a7abfee4

She wasn't part of their regular group of friends.  Then, as now, it's about knowing people.  

It's also about being male.  If these men were women, their underage and excessive drinking would be prominently featured in everything that's being said about them, rather than duly noted.  

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